It'll still work with PowerVR SGL games?
Yes, and it'll still work with PowerVR MiniGL drivers for select id Tech2 engine games as well. The PowerVR HAL checkbox is only a Direct3D override. With your plans, I suppose you can keep that permanently unchecked.
The s3 Trio is sharper in VGA output than the Geforce2 😜 I hear the Geforce4MX is a better subsitute. It's just a Geforce2 that sucks a little less.
As for PCX-2 game compatibility, the last game to ever support it directly is Metal Fatigue, a 2000 mecha RTS game. The only Unreal engine games to support PowerVR is Unreal, TNN Outdoor Pro Hunter and Klingon Honor Guard (despite SGLDrv existing in everything after UT it's regressed against Core.dll. i've emailed tim sweeney about that already). The only id Tech 2 games that support PowerVR are Quake, Hexen II, Quake2, Half-Life, and SiN (no Kingpin, Heretic II or Soldier of Fortune here)
Of course had there been a Opengl32.dll hook that passes all triangle strip calls to translate to straight triangles for the PowerVR MiniGL it'd probably have better luck with id Tech 3. The MiniGL has no calls for any strips