As mentioned earlier, I have now tested the other 2 titles.
Colin McRae: DiRT (EAX5)
WXP:
XFTI_PCDRV_LB_2_17_0008.exe
W7:
DanielK 5.0
Game has a very similar build to Race Driver GRID ("reviewed" above). It is from the same developer/publisher (Codemasters) and slightly older. Being slightly older and therefore closer in time to Vista release, they thought it would be a good idea to have dedicated DS3D/OAL switch in game audio settings. In later Race Driver GRID this is missing and the switching is done behind the scenes automatically.
I haven't noticed any difference using OAL between WXP and W7, both were fine.
The DS3D version (which I have only tried in WXP) seemed fine but I think it had an issue with having your car louder than the opponents. This was more apparent in replays. Not really a big issue but technically this makes the OAL implementation slightly better (which works fine in both WXP and W7).
As previously, I have not made any recordings and only used my senses/memory. Overall the positioning seemed a little worse than in Race Driver GRID which was already average.
TimeShift (EAX5)
WXP:
XFTI_PCDRV_LB_2_17_0008.exe
W7:
DanielK 5.0
Audio and positioning sounded the same in WXP and W7. Overall the positioning is on the better side.
Conclusions
Look closely at the release dates:
Windows Vista ... 2007-01
Colin McRae: DiRT ... 2007-06
Bioshock ... 2007-08
TimeShift ... 2007-10
Unreal Tournament III ... 2007-11
Race Driver GRID ... 2008-05
General findings is that everything works fine in W7 - except for Race Driver GRID which could maybe be fixed by downgrading the DanielK drivers since it breaks the same way on latest WXP drivers from Creative and they require downgrade to make it work.
These games probably work fine because they were released after Vista was released. If you were a game sound engineer back then, you have probably heard about Vista dropping some important audio tech. To me it seems like the devs knew about the issues by the time Vista dropped and prepared their games accordingly.
This is generally good news because Windows 7 has support for DSR, scanline-sync (RTSS) and is usually the cut-off "old" system for various community mods. Just bring the supported sound cards from the XP days to have similar experience to mine in Windows 7. These Vista-era games should provide great gaming overall in W7. I have only tested a handful of games but I am confident the situation will be similar with titles like these. I would still be wary of running DS3D/EAX games on W7 that were released before Vista. It is something I plan to look into as well.
I would also like to mention that some of the games ran better and seemed more stable on WXP, in terms of FPS, frametimes and random slowdowns. This may or may not be an issue for you or your use case. I have usually maxed out the in-game graphics settings and NVPI AA, at around 2560x1920 - so if the game has intense graphics this can be expected, you just need to lower them somewhat. You can also run the latest and greatest graphics cards in Windows 7 so that might take care of those pesky performance issues as well.