Q is the brightness, R is supposed to be brighter than Q but isn't always.
3 is the color, 2 should be a little warmer, 2, 3, and 4 are the good bins, which you like is a matter of preference.
Don't believe the bin ratings too much, they vary all over the place. Think of them as sort of a rough guide.
Q3 is pretty good. Trying to change out a LED on an already assembled sandwich probably isn't a great idea.
I wouldn't put an S or T into a minimag. It's only worthwhile if you run it at 3 watts, and then it will get too hot, and getting enough power to it from alkaline AA's will be marginal. If you want to run at 3 watts, you need a better host than the Minimag.
If you really want a step up in brightness in a LED light, I think you have to give up on the Minimag. Look into a Surefire L4 or L5 something like that instead. If you want an absolute monster, look for a used Space Needle II which is based on a Mag 2C. But they are kind of scarce these days.