Hmm well after running Xbench with and without Quartz 2D Extreme enabled, I'm not sure why Apple decided to disable it (at least on my machine) unless they disabled it on everyone's. At any rate, here are some XBench's with 2D disabled/enabled. Clearly there's a significant performance improvement when running 2D extreme. I've also figured out how to enable it permanently: spotlight for "Quartz Debug" and run it, then go to the tools menu and click "Enable Quartz 2D Extreme". You'll then need to kill -9 the debug process (or just force quit from the activity monitor), and the settings stick. If you don't force quit, then it turns it back off.
Very strange.
DISABLED:
Results 158.03
System Info
Xbench Version 1.1.3
System Version 10.4 (8A428)
Physical RAM 1024 MB
Model PowerBook5,7
Processor PowerPC G4 @ 1.67 GHz
L1 Cache 32K (instruction), 32K (data)
L2 Cache 512K @ 1.67 GHz
Bus Frequency 167 MHz
Video Card ATY,RV360M11
Drive Type ST9100823A
Quartz Graphics Test 130.23
Line 101.17 2.58 Klines/sec [50% alpha]
Rectangle 110.06 7.74 Krects/sec [50% alpha]
Circle 128.47 2.96 Kcircles/sec [50% alpha]
Bezier 146.95 1.60 Kbeziers/sec [50% alpha]
Text 206.93 3.37 Kchars/sec
User Interface Test 200.93
Elements 200.93 64.63 refresh/sec
ENABLED:
Results 185.84
System Info
Xbench Version 1.1.3
System Version 10.4 (8A428)
Physical RAM 1024 MB
Model PowerBook5,7
Processor PowerPC G4 @ 1.67 GHz
L1 Cache 32K (instruction), 32K (data)
L2 Cache 512K @ 1.67 GHz
Bus Frequency 167 MHz
Video Card ATY,RV360M11
Drive Type ST9100823A
Quartz Graphics Test 180.91
Line 175.57 4.47 Klines/sec [50% alpha]
Rectangle 190.65 13.41 Krects/sec [50% alpha]
Circle 230.03 5.30 Kcircles/sec [50% alpha]
Bezier 145.21 1.58 Kbeziers/sec [50% alpha]
Text 183.03 2.98 Kchars/sec
User Interface Test 191.04
Elements 191.04 61.45 refresh/sec