I've noticed no big changes in 338 over 337 but I've only tested GTA:VCS so far. fps went up by 1 but nothing too noteworthy. Too lazy to revert the stuff in TortoiseSVN so I'll wait for the next SVN to do some more testing.
Edit: Just got 339 and compiling it right now
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AMD Athlon 64 X2 3800+ 2.0Ghz
MSI K8N Neo 4
Nvidia GeForce 8600GT 512MB
4x512MB DDR1 PC-3200
Windows Vista Ultimate 64-bit SP1
Windows XP x64 SP2