There appears to be a VERY common misunderstanding of those numbers by many members here.
The numbers are little to NO use in determining how hard to hit the ball as the only thing they indicate is how much of the ball is buried. The most important factor is WHAT they are buried in.
30/40 sand plays a helluva lot different to 30/40 mulch or 30/40 light weeds.
I'm sorry but there are no short-cuts, you have to learn EVERY shot from EVERY type of rough, (or avoid the rough entirely), with ALL the different club / ball combos you use. Of course starting with the club you're most likely to use from rough i.e. your 64W wedge.