It really comes down to what one is looking for...a WUXGA screen was not an option on T60p, although it can be retrofitted, and neither were SD card reader or IEEE1394 ports. I also find the Z series design to be far prettier than the widescreen T6x series, but that's just me. Performance-wise, it's the same platform, no differences there, SATA I and 3GB hardware limits apply to both.
On a whole different aspect, it's hard to beat a well-preserved T60p with a FlexView LCD if one is into the 4:3 format.
...Knowledge is a deadly friend when no one sets the rules...(King Crimson)
George (your friendly FlexView farmer)
Collecting SSDI: A31p, X24,
Abused daily: T43pSF, R60F, X60T
On the way out/for sale: R60, R61, T42, T43p, T60, T61, T61p, X61, Z61m Ti