EDIT: Dude, nylon tips? Seriously?Why not? I break wooden tips in a couple of days even if I'm just practicing or playing for fun.
I don't play metal but sometimes I play loud as shit and I haven't broken a stick in years. First of all, if you're playing with 7As, I can understand you breaking sticks a lot. Chances are they're way too thin for you. 5As are usually a better thickness for most people. I personally use Vic Firth HD4s (barrel tip), Vic Firth Stanton Moores (big teardrop tip), and Vic Firth Peter Erskine Ride Sticks (for jazz, small teardrop tip). The tips wear out after a few months, which is a decent amount of time, and that's when I usually replace the sticks for lack of stick definition on a ride cymbal.
If you're playing metal, chances are you don't care about stick definition and thus the tip doesn't really matter. I don't even know how you wear down a tip without wearing down the stick first. Is this what's happening?
I used to play with Vic Firth NOVA 7As, and I'm not completely sure what was happening, but oftentimes I would find half of the tip missing after playing a song, and this happened before the stick wore down too much. Then again, often the stick never wore down too much because they had a tendency to split in two before that, so it might be that they were just as high quality as you would expect for the price.
These days I'm using the Mike Portnoy signature sticks (which are a bit bigger than standard 7A, but closer to 7A than 5A) and I usually replace them with new ones after 4-6 months.
I'm playing mostly metal, but also funk and sometimes rock, punk or fusion. I have found the nylon tips good enough for everything so far.