here is the order (top= worst)
x800
x800 GTO
x800 GTO 2
x800 PRO
x800 XL
x800 XT
x800 XT PE
i think thats right, the GTO's might be out of place, umm everything x800 XL or below has 12 pipes instead of 16, lower clock and memory speeds and some have 2.0ns memory instead of 1.6ns memory, for best bang for the buck id have to say x800 PRO and unlock it to 16 pipes, or mabey a x800 GTO2 if you have PCI-E
x800 pro factors:
-If vivo, unlockable to 16 pipes
-a lot can go to x800 xt pe speeds
x800 GTO2 factors:
-can unlock to 16 pipes
-a lot can be flashed to an x850 xt pe
-iv heard new batches are NOT unlockable
someone correct me if im wrong on something, i dont know it all perfectly
EDIT:
Heres a chart, dont mind the pricing since the pricing is out of date