[Bobolto]

My GF has a 2002 Ace 750. When I had my Spirit 750, 85mph felt like the bike was giving it all it had. We are contemplating riding the bikes out to California for a coastal trip this summer, but I'm concerned about riding 80-85mph for 4-6 hours straight (West Texas has 85mph speed limits).

Am I just over thinking this, or is this a bad idea on her bike?

I don't think the Honda 750 was intended or designed to be doing 85mph for hours on end. Yes it can do it and may not harm the bike but i think the Bikes were designed to do 65-70 as the highway speed. Don't think you'd be doing your 750 any favors holding it open at 85mph for 4-6 hours.
Just my opinion as someone who happens to own one.

 

[Bobolto]

You don't have to ride to the speed limit. I'd suggest 65-70mph giving her room to downshift to accelerate for passing, keeping engine and tire heat down, fuel mileage and enjoying the scenery and ride.

^+++++1