Yes they are and No there is no betas yet. The 64 bit system is pretty solid so far I have yet to get my hands on the newest one ( damn sat internet keeps cutting off half way throught ) ( its time to install get right! ) Really there is no advantage yet since 64 bit software is very rare and i mean VERY rare ( unless its for Linux )
I'm running it now myself and having a pretty good time with it. I set it up as a dual boot os on my second computer. 3d benchmarks are about 1000 points less than the XP partition but completely stable. I expected worse than that since there are only beta drivers. I haven't run any actual games because I can't get drivers for the soundcard yet so it wouldn't be much fun. Comparing bm's between the 2 os's gives me something to do though.
Via posted audio drivers yesterday, and they work quite nicely. Overall I'm pretty impressed considering I don't have any 64 bit software yet. I get about 1,000 points less on 3d Mark 2001se and 03, not bad considering it's all 32 bit and the drivers are all beta. Can't wait for some apps to really test it's meddle.
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