This is a good place to start:
http://www.a2asimulations.com/forum/viewtopic.php?f=17&t=10091Here's a quote:
Here is a list of the Bdg.txt big performance impacts. You may need to trade quality for performance:
ENABLE_AUTO_GEN=OFF
MULTI_SKIN_MODE=DISABLE
LANDSCAPE_TEXTURE_SIZE = 1024
Do_You_Want_Flak_And_AAA_Fire=OFF
Collision_Detection_And_Avoidance=OFF
Here is a list of the GUI big performance impacts. You may need to trade quality for performance:
horizon distance = medium (saves 15%) or low
weather = medium or low
particle density = Medium or low
Object Density = medium or low
Object Quality = medium or low
Water = medium or low
That post and the manual give more information about editing bdg.txt.
For problems around AA tracer animation, use particle density; for
problems with large numbers of LW aircraft, (the RAF have far fewer
texture variants) look at Multiskin. Every machine is a different
combination, so tuning is likewise unique to the machine. Play around
a bit, and check back if you need more results, and we can dig further.