I guess I'll really only know if the added hopper size is too much for me once I get the gun and play around with it. I'm involved with HvZ (Humans vs. Zombies at Penn State), and while from last semester I'm known as "the heavy" for being armed with 3 or more weapons, I still have to be able to move with at least decent speed.
I'm a bit of a noob at modding Nerf guns, so please excuse me if something I say here is intensely retarded, but I have read this entire topic, from start to finish, and I appreciate all the work you guys are putting into experimenting with the gun and posting your results for everyone.
For the problem of the gun not being strong enough to pull the 50 shot belt through, why not just enlarge the hopper, so it can fit the double belt? Pulling the belt from the hopper has got to take less force than pulling the belt when its hanging to the floor. And whether its the 25 or 50 shot belt, I'm wondering if adding a hopper on the other side to collect the spent belt would be a good idea or not. On one hand you don't have to worry about where the belt is, if you're gonna trip on it, etc. On the other hand it would make the gun that much bigger... I do like the idea of the belt circling around that VisionCloud suggested, I think it merits consideration. I'm definitely shorting the switch for the lid sensor when I get mine, its sounds like a pain.
On a funny note, from your first post Splitlip, it appears we have the same gaming keyboard (G15).