trag: There are a few ways to get to 40 MHz. The simplest, which is to add a 20 MHz crystal oscillator, seems to work best regardless of VRAM, plus I've seen instances where even faster VRAM doesn't make a difference. Sometimes it's just something on the motherboard which doesn't want to run faster.

For reference, this is how I've done most of them:

http://mail-index.netbsd.org/port-mac68k/2002/05/31/0006.html

And here's the site that had the original information (from archive.org):

https://web.archive.org/web/20040715065245/http://gabezing.sytes.net/LC475-40Mhz-E.html

I've also tried the non-oscillator speedup, but have had more variations in measured speed and more video issues. Here it is for reference:

http://www.applefool.com/clockchipping/q605_40.html

ArmorAlley: Yes, it's most likely your VGA adapter. Try a different one. I can get 1152x870 at 256 colors with generic adapters and 512K VRAM SIMMs.