Max, you need to be a little careful because while there is definitely correlation between swingspeed and loading, swing speed itself is not enough to fully describe a shaft choice.

Don't get me wrong, swing speed is probably the largest variable and should really be the starting point for your choice of shaft. Do be aware that what one company calls a "regular" can be very different from what another one calls a regular -- it doesn't even have to change from company to company, different models from the same company can even be significantly different on this. The good news is that today almost every shaft manufacturer puts their swing speed guidelines on their websites, so you can find this information reasonable easy.

Now, with the swingspeed out of the way, let's look at "loading". The speed is a significant portion of this, but, a players transition from backswing to forward swing is also important. There are some players who make a very smooth transition -- almost or even actually coming to a complete stop after backswinging before forward swinging. These players may actually need a flex less than their swing speed would indicate because of the slow transition. On the other hand, there are some players who make a very sharp, violent, quick transition from back swing to forward swing -- these players may need a flex stronger because of the quick reversal in their transition.

Lastly, the all-elusive variable of feel is truly important. A player needs to like the feel in his clubs to be the most confident in them. I call it all-elusive because what I like in feel may be very different from what you like in feel, even if we have very similar swings. For a lot of people, this last variable can override other. I have an acquaintance who swings his driver 105 mph or so, but really likes regular shafts. He says he just loses feel with anything stiffer, so that's what he plays.

Even then, all that said, a good clubmaker can also trim a shaft to a desired flex. A shaft can be trimmed to be left a little stiffer and/or weight added to the clubhead to make a shaft play a little weaker. So, if you find a shaft you like, but are right between the speed guidelines, a good clubmaker can make the shaft flex right where you need it to be. So, there are lots of options out there.

The big thing, like was said above, is to go and get your swing speed measured. It can be guessed, sort of, by posting your club's distances, but that isn't super accurate because not all iron sets are made the same. But, nothing beats having actual measurements.