Sounds like you're doing something very wrong. The JPG quality setting has no bearing on render speed whatsoever. The images are not even being stored in JPG format in VRAM
I didn't realise that Gabriel?... my models are just bog-standard .b3d's... no `on-the-fly` loading involved at all... and when I reduced the texture sizes I did get a definate increase in frame-rate??... I assumed it was cos the sizes of them was clogging my systems memory up!... it must have been something else causing it!... it has reduced the end file size though ;) lol