From personal experience with having 4.30, 4.10, and 3.91 in my car, and seeing no performance difference, I would be more conservative with the gear choice. A 500 shouldn't need more than a 3.73, and 3.91 is as low as I would go.
No problem with the 950, as long as it's not a 750 venturi carb with a 950 label slapped on it (holley has done that).
A cam swap would do wonders.
You could run a compression check to get a vague idea of compression ratio.