Hi Challenger,
I, too, stopped driving over 80mph on the way to work when I got the HCH. I now drive at 73mph, and have a 160 miles round-trip commute, which is mostly cruise-control on the highway. I have had my '04 HCH MT up to 95mph so far.
I have a lifetime average of 48.4mpg, so it seems you're on target anyway. I've put 47 tankfulls so far.

C' ya!