+1 on the synthetic to conventional myth. you can switch back and forth all you want.
dont quote me on this, but i think most people are using synthetic 5w40 or so for the supercharged engines. im pretty sure you want something nice and thick, but you still need to take care of your cold starts (the 5w part). as far as i know, there are no conventional 5w40's. you would have to go 10w40. I think the stock supercharged stangs (cobra and gt500 and such) can handle 5w50. otherwise i think some people use 5w40 rotella, which is technically a diesel oil. but still good stuff for a mustang.
as for synthetic blends, my understanding is that you really dont benefit from them. i only use it because i like motorcraft oil and it happens to be a synth blend. otherwise i would be using a synthetic. i may switch back to a full synthetic when i either have a better paycheck, or decide that the synth blend isnt clean enough. but so far so good.
2002 GT 5sp. 16x,xxx miles
Steeda Exhaust, C&L plenum, BBK Throttle Body, Steeda Underdrive, Steeda short throw, unknown stage clutch. Rear main leak. Compressor seal leak. Steeda lower control arms. good tires.