SMG progressively getting slower

[JMC47]

While that is a good suggestion, I think I can tell you better what's happening. A lot of time, OpenGL specifically can cache a lot of stuff and that makes it get slower over time. I think D3D does it as well, so you could try flicking the texture cache settings to see if that fixes the speed. Just flick to safe and back to whatever you were at to clear it.