Collecting has been "sweet" for these Set Registry enthusiasts.

Hardcore fans of the gridiron legend known as "Sweetness", these hobbyists have worked diligently towards completing their Walter Payton Basic (12 cards) and Master (109 cards) sets.

"He was one of my all-time favorite football players and really the whole reason why I started collecting cards," said Mike King, an Ohio native who owns the No. 2 Payton Master set.

Randy Hoehn, an Illinois-based enthusiast who sat in the first row on the 50-yard line for Payton's memorial service at Soldier Field, shares King's passion for the late running back.

"Wally was my idol back in the 1970s . . . I've just been a Walter fan ever since he came out of Jackson State," he said.

It's this type of devotion that's inspired these hobbyists. And, of course, a key to any player set is a high-grade rookie. The Hall of Fame running back's cardboard debut was in 1976 Topps (#148). Hobbyists say it's not an easy single to find in pristine condition. Of the more than 3,200 sent in to PSA, only about 10% have been graded PSA 9 or better.

"Like any other card from the '70s, most have centering issues, printing issues or corner wear," said King of the Payton rookie.

Hoehn, who has just submitted two rookies to PSA for evaluation, agrees.

"They're really off-center (left to right) front and back," he said.

But other Payton enthusiasts insist that if you have the money, mint rookies are readily available.

"Compared to some of the other tough cards, finding a high-grade Payton rookie is actually pretty easy," said Stephen Barr, an Oklahoma-based collector who owns the No. 1 Basic and Master Payton sets.

Collectors agree that the 1976 MSA Saga Disc is more elusive than his Topps rookie. Created as a Philadelphia School District promotion, these discs were distributed with school lunches. The front of these discs showcase colored borders and four black stars across the top. Personal information, such as height, weight and date of birth is displayed in the border area, while a black and white photo is featured in the middle of the front. The backs boast a Saga ad, as well as a slogan that says, "Nutrition is body ecology."

"The Saga discs, as a whole, were of very limited production with a narrow, local, regional release," said Barr.

So far only six Saga discs have been submitted to PSA and there has yet to be a PSA 10 example.

Two other tough singles to uncover in mint condition are Payton's 1977 Topps Mexican cards (regular card (#360) and rushing leaders card (#3)). With text in Spanish, the Mexican series is a 528-card set. Cut in a different manner and produced in smaller quantities than the regular Topps series, many of these cards were released in two-card packs that came with gum. As a result, these cards are notorious for gum stains.

"The Mexican release is tough for a variety of reasons . . . But it seems to be a combination of relatively limited production (especially low availability in the U.S.), a scarcity of unopened material, the lower quality used to produce them, and the way in which they were packaged," said Barr.

No examples of Payton's regular Mexican card have graded higher than a PSA 8, while only four copies of his rushing leaders single have been deemed PSA 8 or better.

Another difficult card to obtain in high-grade is Payton's 1978 Topps Holsum issue (#2). Distributed with loaves of Holsum bread, these singles boast a color photo of the player on the front accompanied by their name, team, and position. Their backs are predominately green and yellow and feature personal statistics (height, weight, etc.), a short list of career highlights and a quiz question.

"They were hard to find really centered well," said Hoehn, who owns two raw examples that he plans to submit for grading.

Barr concurs, "The Holsums also seem to be affected by a combination of limited production, rarity of high quality, untouched raw condition cards and centering problems."

A more mainstream Payton that's difficult to uncover in pristine condition is his regular 1985 Topps single (#33). Despite an abundance of raw cards, there has yet to be a PSA 10 example. Hoehn attributes this to the card's unforgiving black borders.

"Any time you rub the edges on those black borders, the white paper underneath starts to show," he said.

Larry Parten, a Mississippi-based hobbyist who owns the No. 11 Basic set, agrees.

"The black card (1985 Topps) is beautiful, but is extremely hard to find in high-grade," he said.

A PSA 10 1985 Topps card is the only single that stands in the way of Barr having every card in the Payton Basic Set in gem mint condition.

"It's down to just the 1985 Topps to complete a straight PSA 10 set," said Barr, adding that he expects "a huge amount of competition" for that card, not only from Payton collectors but from 1985 Topps collectors as well.

Another elusive item is Payton's 1987 Ace Fact Pack issue. Shaped like playing cards and distributed in the United Kingdom (U.K.), these cards feature a photo and personal information about each player. To obtain the Payton card, hobbyists initially had to purchase the Bears team set. Just 15 1987 Ace Fact Pack Paytons have been graded by PSA; ten cards have received a PSA 10 grade.

When their collections are complete, some of these hobbyists plan to give them to their children and grandchildren.

"About two and a half years ago, my wife gave birth to our first child - a son," said Parten, "and I want him to know about the best running back of all-time, and have a small piece of history as well, with the cards."

Hoehn has similar aspirations for his set.

"My daughter just had twin grandsons last year. They just turned a year old the other day. It's just something that I want do for them really," he said of collecting the Payton sets.

And what could be "sweeter" than sharing memories - not to mention a registry set - with your children or grandchildren?