Eh a 5900U underperforms a 9600XT in Oblivion by quite a bit. I've run both and I promise a 9600XT can play Oblivion acceptably at 640x480. I have video of the fun I recorded with my 5950 years ago.
https://www.youtube.com/watch?v=qzDZhb808ts
FEAR is the same story. Though I should have run 640x480.
https://www.youtube.com/watch?v=0rlZb6YsJOQ
Here's Half Life 2 D3D8 vs 9.
https://www.youtube.com/watch?v=KwUxxLzu-uk
STALKER in its static lighting mode (D3D8). This interested me because this game started development during NV3x days and was initially advertised with NV3x in mind.
https://www.youtube.com/watch?v=OOneA51UdEo
The problem is any game that uses pixel shader 2 is hopeless even on NV35. FEAR has a D3D8 shader option, HL2 defaults to D3D8 on NV3x, and Oblivion is entirely PS2.0 with some extra 3.0 in some cases.
FarCry runs a mix of D3D8 and 9. The console tells all, I believe. Halo might default to D3D8 with FX but I don't recall anymore.