Here's some new results. I ran a test today on the same machine. One boot is Tiger the other is Leo.

3GHz 8-core, Mtron, x1900

In tiger I was running 14 layers DV. The frame rate counter on layers 11, 12, 13, and 14 were faltering showing as low as 15.

In Leo 10.5.1 I was running 8 layers and 6,7,8 were all dropping to 15.
In Leo 10.5.2 I was running 10 layers and 9,10 were dropping to 15.
I added the "Graphics Update" to 10.5.2 and I jumped up to 12 layers where 10,11,12 were dropping to 15.

On all layers I was running Visual FX and Color FX.

Turning off the FX, the performance jumped to:
Tiger was 14 layers
Leo 10.5.1 was 9 layers
Leo 10.5.2 was 11 layers
"Graphics Update" was 13 layers.

All in all, Leo is still not as strong as Tiger but I also didn't have time to shut off all the extra crap in this instance of Leo yet. I'll report after I do.