You're killing synchro's because of the RPM you're shifting at. Not many manual tranny's will shift above about 6500 RPM unless you pro-shift them. And if you pro-shift them, you will tear synchro's up NOT shifting fast at high RPM's.

If you're breaking shift forks, it sounds like you may need to adjust the shifter a bit tighter because there's really no load on a shift fork other than overextending when shifting.