David,
Can you post all the cam specs?
I say you're on the right track with the spring pressures. If it's a race car, you're already of the mindset that you'll be doing maintenance. If it's a billet camshaft, I'd run some good pressure on it. It won't hurt it.
I just did a 347 for a 7.50 1/8th mile car. It peaked at 6500 as well with a solid roller...236/242 @ .050", .600" lift. I installed 250 seat and 600 open pressure on those heads and used the lightened steel retainers.
Of course the lighter the valvetrain, the more you can get away with on spring pressures. But I have minimums that I use with different cams.
Valve float is not your friend....and if you decide to stay in the gas a little longer before going through the lights, or before braking in a straight, I'd rather not worry about losing control of the valvetrain. It's not fun when that exhaust valve hangs open longer than it should.
