Valves for rear-wheel suck up

I have a kit that came with 8 1/2 inch valves. I heard that the 1/2 inch on the dump side will be to fast and it will be hard to adjust drive height. I was thinking of getting 4 more 3/8 valves and using those for the dumps instead and take the left over 1/2 inch so that I can suck up the rear wheel. Will the 1/2 inch valves be to fast for that?