I like to shoot for the best quench I can get even if it means a tad higher comp. The best quench is of course in the .040 to .042 area. Are you running aluminum heads ? At .049 you will still have a little quench. My quench is about .046 and I have 10.6 comp with my aluminum Indy EZ heads and I have no spark knock or ping at all with 37 degrees total. If its aluminum heads I would try to keep it about 11.0 at the highest as it will also depend on the cam you use. Iron heads I like to keep at 10.0 and this is with quench on both heads. If you can get it in the .045 area and no more then 11.0 thats what I would shoot for but even at .049 you may get away with it depending on the cam for cyl pressure. Ron