How much highway time will your car see? I ran a stalled, reverse manual valve bodied C4 in a street and strip car for about 4 years with 4.10s. It was bearable when I was younger to be hitting 3k at 60mph but I am not sure how I would feel about that horrible drone today. I drove that thing everywhere though and beat the crap out of it for nearly 50k before drive started slipping when it got traded out. As for a C6, if you are going to go for this may as well go TH400. Depending on your power goals a built AOD may not be a bad option, my AODE has taken 30k of abuse from my current setup without a hiccup, just got to remember to change its filter and fluid on a regular basis, I do mine every 10k.