If you want a real bright LED light, see if a Surefire L4 (2x123, 5 watt) will fit in that slot.

Otherwise, the high class replacement for the Minimag is the Arc LSH-P (1 watt) with the 2AA battery pack (they have a pushbutton version and an out-of-production twist-on version that you can buy used on CPF if you ask). It will run for around 5 hours on a pair of L91 lithium Energizers and should fit in that Minimag slot. It's expensive, but you said you wanted high end.

You can also get an LED drop-in module for the Minimag. The Opalec Newbeam is terrific according to everyone who uses it. It's less bright than the stock Minimag and has a wider beam, but it runs for a very long time on two AA's and the brightness doesn't diminish til the very end. There are also high powered "sandwich" modules with Luxeon LED's (www.anlighten.com/shop). These in my opinion are a bit finicky--they tend to fall out of the light when you change batteries, which can be a hassle if you forget to watch out for it. But they work pretty well.

I'm not familiar with that specific pouch so I don't know what other lights will or won't fit in it.

As 03lab says, you can find out way more than you wanted on this subject over on CPF. He and I are both regulars there.