I run 5 3/4 to 6 1/4 in my D2585's in our Heritage Jrfueler, but most of the time I run 6 lbs on my 12" wide wheels. When I'm looking for more tire speed I lower the pressure, more bite more pressure.
On the other side 6 3/4 was just too much tire spin for our combo [ 870 hp]. The up side for you, running 7 1/2 is less tire wind-up so better RT. I would worry about tire shake, but with lower HP you might be getting the tire speed you need and not pulling the RPM down and getting out of good HP range.
Feel free to call with any questions, 805-444-4489
Jon