Hugo, as a bench mark ; My best ET with 440-1 heads on a 528 is shifting at 7450. On the 1-2, 7350 2-3. As read off my data logger. My shifter is set for 7250, so when you pull the shifter it goes another 200 to 150 rpm. I doubt twelve more cubes would change that much. This is with a custom ground cam designed for the most hp.