Mine at present would be about 255mph in 5th if it ever did 8500rpm.
But mine is tall, largely so the top speed for 1/2 mile or whatever can be done in 5th. A lot of fast cars in the US would have theirs geared to hit top speed in 4th, simply as 4th is the strongest. Doing so would have huge detriment to the lower speed driving though
Even mine is very tall, but I can get away with it due to the large engine. It does drive a little nicer with a shorter diff though.
Do you have a shorter diff option ?