20 pitch VS. 16 pitch on a R&P system

I am designing a 5'x10' plasma table that I hope to finish this summer. I've seen several builds here that use the 1/2" square, 20 pitch, 20 degree pa rails. I would like to use a 3/4" square, 16 pitch, 20 degree pa rail. The price difference is only $15 per rail in the mcmaster catalog. Is there some reason, other than cost, that the 20 pitch rail seems to be preferred?
Thanks
i_r_machinist