I would be happy with a 6.1 engine. In fact, if they were offered side by side (6.1 vs 6.4) and that was the only real difference, then I would opt for the 6.1. Now if the 6.4 came with alot better suspension, throatier exhaust and maybe some minor appearance packages and kept it reasonable in the price upgrade, I may jump on it.
The problem is though I expect the insurance rate jump from a 6.1 to a 6.4 may be very costly over the years and I am not sure it is worth it for a car that will mostly be driven around on the street and maybe raced here and there. Once you start getting over 400HP, you have to ask yourself, how are you really going to use that on the street and how much will more HP get me in trouble.
I am getting to old (and wise) to take to big of a chance in getting in 100+ MPH races or where I could lose my license. In fact, I am just now considering myself "mature" enough to handle having a 6.1 engine!
