Predicting how a spring will behave is pretty simple if the specs are known.
The spring rate (not always given) is in pounds per inch of deflection: how much weight squishes it exactly 1"?
To calculate this from know pressure (like valve closed and valve open to a given lift):
Subtract the closed (lower) pressure from the open pressure, like 208 - 82 = 126 lbs.
Now divide it by the lift, like .396 (the stock 261 lift), and get 318 lbs. per inch. This is how you predict a pressure change with different assembled heights and/or lifts.
Example: adding .100" to the lift increases only the open pressure by 318 (the rate) by .100" (the change) = 31.8 lbs. becomes 240 lbs.
Increasing the assembled height by .050" = 15.9 lbs., so the new pressures are 66 lbs. and 192 lbs.
Generally, a faster-opening cam requires more open pressure - but higher lift generates higher open pressure automatically as above.
Higher engine speed needs somewhat higher closed pressure to stop the valve from bouncing as it closes.
