Too long an installed spring height will lower the rpms where valve float occurs in your engine, and the amount it's lowered cannot be exactly predicted. It depends on the way the cam was ground and the type. You can normally get the correct spring shims from your cam grinder, or from any local engine rebuild shop, just by taking an old one in for comparison.
You can also check your springs for holding pressure by putting a bathroom scales on a drill press. Put a flat metal plate on the scales, add the spring, zero the scales and push down on the spring with the drill press to the 'recommended' installed hight. See if the scales read near the specified 'closed spring pressure' in lbs. If not, push more until you get that wt on the scales, then measure the resulting spring height in thousandths of an inch. This will tell you what shim package you really need on that spring. You're using the drill press as an arbor press, and real racers routinely do this check. Incidently, I applaud your efforts- the 'installed height' thing reoccurs each time a valve or seat grind is done and most guys never bother to check. Then they wonder why their freshly overhauled engine seems lazy....
