its pretty much universally known the 5 speeds are stronger than the 6. It makes sense, b/c you are trying to fit an extra gear in the same space, so things have to get smaller.

Get a 5 speed if you want to launch hard - end of story. I had the same concerns as you a few years ago when I bought my Evo 8. If you find that you still can't deal with the higher revs at cruise, you can obtain an Evo 7 5th gear for a few hundred, which will lower cruising rpm. I was going to do it before I bought the car, but now that I own the car, there are a LOT more things I'd rather do. I think you'll find the same.

Good luck on your purchase