These are the overall benchmark results of running a test notebook in Mathematica 5.0 on various hardware: (higher score = faster)
AMD64 3200+, SUSE Linux 9.0 for AMD64 : 3.55376
Athlon 64 3200+, Revision SH7-C0, 2.25 Ghz, 1MB L2, Windows : 3.5179
Opteron 244 (1,8 GHz), 2GB, SuSE Linux 9 Pro for AMD64 : 3.40254
AMD Athlon 3200+, 2GB RAM, WinXP Pro : 3.23186
Athlon 64 3200+, Revision SH7-C0, 2.0 Ghz, 1MB L2, Windows : 3.1481
AMD Athlon 64 3200+, 512 MB, Windows : 3.02386
Opteron 244 (1,8 GHz), 2GB, Windows XP Pro SP1 : 2.83638
Opteron 244 (1,8 GHz), 2GB, SuSE Linux 9 Pro for i386 : 2.73023
Pentium 4 XT ("Extreme Edition"), 3.2 GHz, 2GB, Win XP Pro : 2.6867
xp-2700, 2.17 GHz, 333 FSB, 1 GB, win-xp-pro : 2.54757
Athlon 2800+, 512 KB cache, 333 MHz FSB, Win XP Pro : 2.50588
Pentium 4, 3.2 GHz, 2 GB, Win XP Pro : 2.48287
Dell Precision 650, 4X3.06GHz Xeon, 512KB L2, 4GB, Win XP Pro V5.1 : 2.43878
P4, 3.2 GHz, 2GB RAM, 512kb, XP SP1 : 2.41661
IBM ThinkPad T41, Pentium M 1.7 GHz, 2.0 GB RAM, Win XP Pro : 2.39752
SGI Altix 3300, 1.3 GHz, 19 GB, Linux : 2.22437
P4-B, 3Ghz, 4GB, W2K3 : 2.1325
Mac G5, 2GHz dual, 1.5GB RAM, OS X 10.3 : 2.08193
The Thinkpad Pentium M, even with bottlenecks which are inherent in laptops, scores higher than the dual Powermac G5. The test notebook includes calculations like
Timing[PrimeQ[2^9689 - 1]][[1]]
Timing[N[Pi, 800000]][[1]]
See more at
http://smc.vnet.net/timings50.html