Comment # 5 on bug 941031 from Tom���� Chv��tal

It is related to your graphic card. Basically there might be some bugs in
nivida driver that causes high cpu usage. Which you avoid in raster/opengl
settings as it gets more offloaded to your card.

Thus I would close this as CANTFIX as we can't really alter the binary blob.
You can try reporting it to nvidia as they are only ones that can fix it :)