You are wrong about Gamestudio being "slow" for shaders.. it has nothing to do with A6 engine(except on BSP blocks). Nor can you compare Doom3 and Sphere, as they are entirely different. Sphere is going to run a good deal sower than Doom3 for several reasons: it does a lot more, and it is not as optimized for old hardware. Sphere is more than a bunch of shaders stuck together..

it not the shaders themselves that are slow, it's the rendering of shadows and such, which are very polygon and fill-rate intensive. Doom 3 uses an entirely different shadowing method, which only produces hard shadows.. you can decide what you like better, but I prefer soft shadows. Doom3 also uses the most basic shader version, in optimzed assembly code. Sphere uses shader model 2 and HLSL, which allows you to do a lot more, but sometimes it is not optimzed for older hardware.

I cant belive anyone would like Halfe2 better than Doom3.. HL2 is very plain looking and boxy, with basic phot based textures and not much in terms of lighting and such. The artwork is mostly this ugly sewers and industrial stuff.. looks New Jersy or somehting.. I'm sorry but if i want to see that I can go outside and to the dirty river near my house.