today's six cylinder cars can run rings around [most of] our old muscle, in stock form.
but with that said, "i coulda had a V8" seems to be a reasonable conclusion after a guy figures out the minute difference in both cost and transplant installation differences.
plus, as the older 5.7's are [somewhat] cheap these days, and will run great even with a ton of miles on them, the 8 gets my vote.
unless, of course, you already have the 3.6 and the necessary wiring to do the install.