#1
Can Anyone tell me if there is a major difference between Celestion GT12T-75 watt speaker and Vintage 30's, other than the obvious power handling difference

is the tone much different between the two?

and i've got a 6505+ head, with 4, 8 and 16ohm switching, but how does this affect the cab, as im only going to use it as a half stack, what impedance should i get on the cab?
#2
They have completely different voicings.

most people like to use 16 ohm cabs. Setting your head to 16 ohms uses more windings on the output transformer which results in a bigger low end. Sometimes its more noticeable, other times it isn't.