My two cents:
I have ordered from the Gum Rubber people Pelleteer mentioned and they were good to do business with. I have some of their material and it shoots real good. It comes in the natural rubber colour and its elasticity, cast, and durability were very good.
I bought a 5-band sampler from Flatband some time ago and have nothing but good to say about his sets. Great rubber, cutting, and probably the best pockets I've seen. (No slight to any of the other vendors and I make all my own now, so that's why I haven't tried any of yours.) I've seen kill shots with Perry's and BB's stuff. I know BB has to put out a good set with all the kill shots I've seen online. And I've seen a lot of good reviews of Perry's stuff. So take your pick.
I went through a gum-rubber stage whilst on my search for the perfect elastic. I like it more than any of the other flatband materials but what I don't like is having to either cut my own (I suck terribly at cutting flatbands, even with a rotary cutter) or buying from someone (I believe in making all my own kit). I have since moved on to Mexican-style chained rubber bands made from high-quality rubber bands and have found my dream elastic with a 50-yard effective range. Yes, I know they look like something recovered by police after a riot in a third-world country but they shoot like a dream.
The cans moved so far when Rufus shot them for a variety of reasons. First, he shot rocks which spin/rotate as they pass through the air. His bands were sized perfectly to his size of ammunition and did not propel them too fast. You will see his bands are not stretched to their absolute limits on his videos. This kept the speed low but the momentum of a spinning stone at around 140-160 fps has to be pretty good. If they weren't spinning I think they would have just punched through. As a product of the Depression and rural South he would have been doing his absolute best to gain the maximum amount of use from his bands per set. All of these combined to form his perfect bandset. I don't think he could have shot effectively at 40 yards but I wouldn't stand out there at that range and call him mean names, either.
thanks for looking