[thejeff]

Actually I ran some tests comparing turn time hosting with graphics in test mode.

Athlon 1.8G 1G Ram running Linux
Early Era, all nations Large random map.

By turn 10-12, regular turn generation time was up around 1 minute.

I copied the save and generated the turn 5 times using the GUI and 5 times in text mode. The text mode had a slight advantage, but nothing significant.
Now if your video card is already thrashing just drawing the background animation, then that may bring the whole system to a crawl, but it doesn't look like there's anything specific to updating the graphics slowing turns down.

GUI tests:
1:00
1:22
1:16
1:23
1:36
Average: 1:19.4

Text tests:
1:08
1:11
1:13
1:20
1:35
Average: 1:17.4