If the springs are the Indy G928's, that's a completely different spring.
When they stopped using Comp springs, I remember there was a period of time when you didn't really know exactly what you'd get when you ordered them with the "928" springs.
Most of the time though, they were a pretty high rate spring that would be over 400lbs @.650 lift if installed at 1.900.

I would have expected the motor to peak closer to 6700 if the valvetrain was rock solid, and would have likely only been down a few hp @7k....... But that assumes you had pretty stout springs in it.
And, that's also assuming the intake behaved similarly to the 440-2 in the upper rpm's.

Before I messed with the installed height, I'd find out what the open pressure is now.
If its already in the 400lb range....... I'd probably just live with it for a street application.


Edit- I see in your first post you say the spring loads are 150 closed/370@.620 lift...... Which works out to 354lbs/in........ Which is what the Comp 928's are....... So those are likely what you have.
If they are in fact Comp 928's, I go by my original recommendation of 1.88-1.90 IH.

If it were going in a "race car", I would have used Comp 929's @1.88-1.90.