Edgy's DRI performance halved

System Specs: Dell Inspiron 510m, 256mb ram, Intel 855GM graphics chipset, Ubuntu Edgy

Ubuntu Edgy's version of Xorg/drm/Mesa is giving roughly half the expected DRI performance on my system compared to Dapper.

Using 1024x768@24bit, I get the following results on Edgy:
With powernowd enabled (600Mhz): glxgears ~550fps, ppracer 16-20fps (probably scales up to 1500Mhz due to CPU usage)
With powernowd disabled (1500Mhz): glxgears ~700fps, ppracer 16-20fps. All other 3D applications exhibit bad performance compared to Dapper, whilst 2d remains unaffected.

Expected results (from Dapper or newest Mesa/drm/xf86-video-i810): glxgears gives ~900fps irrespective of cpu scaling state, ppracer ~40fps.

Steps to reproduce:
1. Boot to Dapper LiveCD/system, in a terminal run glxgears -printfps, then repeat again after "sudo /etc/init.d/powernowd stop".
2. Repeat step 1 for Edgy LiveCD/system, noting different speeds.

Partial workaround:
Upgrade to newer Mesa, drm, xf86-video-i810 from git. I have not been successful in compliling xorg-xerver, and as a result certain apps don't function well (tremulous unexpectedly quits, Beryl crashes the X server), while others work fine (e.g. ppracer, at ~40fps). This is possibly due to new functionality in DRM that requires the newer X server to function properly. Is it possible to backport changes in order to restore proper DRI in Edgy's version of Xorg/Mesa?

My /proc/mtrr:
reg00: base=0x00000000 ( 0MB), size= 256MB: write-back, count=1
reg01: base=0x0ff00000 ( 255MB), size= 1MB: uncachable, count=1
reg02: base=0xfeda0000 (4077MB), size= 128KB: write-through, count=1
reg03: base=0xf0000000 (3840MB), size= 128MB: write-combining, count=1

I'll attach system logs, but I believe the source of my problem is indicated in Xorg.0.log:

(WW) I810(0): xf86AllocateGARTMemory: allocation of 8 pages failed
        (Cannot allocate memory)
(II) I810(0): Allocated 32 kB for the logical context at 0x7fe2000.
(WW) I810(0): xf86AllocateGARTMemory: allocation of 768 pages failed
        (Cannot allocate memory)
(II) I810(0): Allocated 3072 kB for the back buffer at 0x7800000.
(WW) I810(0): xf86AllocateGARTMemory: allocation of 768 pages failed
        (Cannot allocate memory)
(II) I810(0): Allocated 3072 kB for the depth buffer at 0x7400000.
(II) I810(0): Allocated 52992 kB for textures at 0x620000
(WW) I810(0): xf86AllocateGARTMemory: allocation of 14593 pages failed
        (Cannot allocate memory)