Frame Rate Questions

I've been performing some tests for an upcoming project which is a multiple tower, multiple projector blend.

The total content size is 2848 x 1440. I have four different tower types and was evaluating each towers ability to playback a file of this size.

The files is as follows
2848 x 1440 Apple intermediate at 30fps data rate is about 212 mbit/s.

All towers had a fresh install of osx 10.6 with all the updates. to 10.6.4
All tests were performed by moving the same SSD content drive from tower to tower.
All tests were on catalyst v 4-257
I would use the hud to select and play each file, the frame rates I reference in the results are the ones observed in the hud.

2006 Eight Core 3.2 - Quadro FX5600 - 30fps
2006 Eight Core 3.2 - GeForce 7300 - 30fps
2006 Four core 2.66 - GeForce 7300 - 15fps
2010 Four core 2.66 FeForce GT120 - 30fps

A couple interesting things:

The 2006 Four core 2.66 towers would also play a second file of the same size at 15fps without any effect on the playback of the first file.

Also when I accidentally had one of the towers set to 25frame playback it would play the test file back at 25fps? but with the tower set to 30fps I only get 15?

It would appear I'm just running up against processor limitations in decoding a file of that size, and my only choices are better servers or having them break up the content into smaller files. Does anyone have any other thoughts or can explain the fact I could get 25fps from the same file with the towers set for 25fps? Is the display in the HUD an accurate report of FPS playback?

Long post, sorry about that, thanks for taking the time to read!

Guy