well, for my engine i recently rescaled all my models down to be much smaller because for some reason i was getting slow down with big models -_- Mind you, i was doing some pretty intensive stuff with ALOT of objects, but i find just making things smaller helped out a fair bit with my speed. But other people here use much bigger models, have cameras zoomed out from between 200-500 from their focused player and get along just fine! So i guess its taste. But its best to choose your scale and try to stick with it before you start.. Scaling all my objects down wasnt fun, even more so when i had to go around adjusting speed stats ect :/
p4 2.4ghz, 256ddr ram, Geforce4 MX 440
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