I use a kitchenaid pasta roller to roll mine out, it's a lot easier on the hands and shoulders to get it really thin using that than it is to do it by hand. The recipe that has the egg whites in it is a classic gumpaste recipe, and it's been around for ages. I've seen variations of it here and there, but it's nothing new. I don't use it because I feel that it dries really brittle, but it's really nice to work with, it handles really well. I use a quick gumpaste that's basically fondant with tylose in it, and I've messed with the recipe until I have it where I like it. I don't know about how the satin ice handles, but the ingredients that are listed are:
Natural and Artificial flavourings
Modified Corn Starch
If you compare that to the ingredients for the satin ice fondant, they're practically exactly the same, but the fondant has more glycerine in it than the gumpaste, and no egg white. Adding less glycerine and more gums will just make it stiffer, so based on how satin ice fondant handles, I'd guess that satin ice gumpaste would be kind of on the dry and stiff side. If you don't add the gelatin you're going to lose some of the stretch, so that could be why it's harder to roll out. Total speculation on my part, though, since I've never used it.
Try the egg white recipe and use corn starch with it if it seems too stretchy for your liking. That will stiffen it up some. I seem to rememebr that I was using the cornstarch with it when I used it, but I prefer to use crisco with the fondant/tylose mixture.