[yrumax]

Relevant hardware:

Shoebox

• AMD 4850e (overclocked to 2.88 ghz)
  
• Geforce 8600 GS
  
• 2 GB ram dual channel
  

Flatbox

• AMD 5050e
  
• (overclocked to 2.88 ghz)
  
• Geforce 8200
  
• 2 GB ram single channel
  

Hard drive 1 boots ubuntu 8.04, kernel 2.6.24-22-generic, Nvidia drivers 180.17, and revision 16823 of XBMC.

Hard drive 2 boots ubuntu 8.1, kernel 2.6.27-11-generic, Nvidia drivers 180.17, and revision 16823 of XBMC.

Test plan:

Playback known functioning difficult x264 rip on shoebox with hard drive 1.

• The Dark Knight "1080p" rip (actual resolution 1920x800)
  
• Section 00:10:25 - 00:10:52
  

Playback killa sample on shoebox with hard drive 1.

Swap hard drives, and repeat test with same hardware booting ubuntu 8.1.

Repeat process above on the hardware on flatbox.

Findings:

Shoebox

• Booting from hard drive 1 (8.04)
  • The Dark Knight sample drops no frames.
    
  • Killa sample drops 202 frames.
    

• Booting form hard drive 2 (8.1)
  • The Dark Knight sample drops no frames.
    
  • Killa sample drops 231 frames.
    

Flatbox

• Booting from hard drive 1 (8.04)
  • The dark knight sample drops 8 frames.
    
  • Killa sample drops 209 frames.
    

• Booting from hard drive 2 (8.1)
  • The Dark Knight sample drops 20 frames.
    
  • Killa sample drops 222 frames.
    

Summary:

While playing back both samples I watched the output of top over an ssh session from another computer. Top had thread view on and was in SMP mode. In hardy and intrepid I saw even distribution of load over two xbmc.bin threads. The load was higher on intrepid for some reason.

tl;dr - According to my tests intrepid takes more cpu power to do the same thing as in hardy.

Other thoughts:

Perhaps the number of frames dropped while playing back the killa sample makes all of this irrelevant. I'll leave that up to you to decide