I've taken a look at these and have a question.

Do you cut away all the excess leather, or leave it?  Seems this would be hugely uncomfortable otherwise.

I have a MTAC, basicaly the same as the Supertuck, the leather will form to your body and keep the gun from rubbing against your skin. its why its there to protect your baby soft skin. you can get  CTAC that does not have the leather on it if you want.

Exactly the opposite; the large area of leather molds to your body, providing stability, support, and comfort.

These holsters appear to be oversized but they really work.

I carry a full size M&P .40 in a horsehide Crossbreed Super Tuck every day, all day long and it's extremely well concealed and easy and comfortable to carry.

Just make sure that you get yourself a proper gun belt to support your rig.

My personal recommendation is to buy yourself a horsehide Crossbreed holster and a 1 1/2" Comp-Tac contoured belt.

IMO; Crossbreed makes the superior, although admittedly uglier, holster but the Comp-Tac belt is better than the Crossbreed product.

I even prefer it to mu Beltman belt.

I own one of each, so I'm speaking from experience rather than out of brand loyalty.

Both Crossbreed and Comp-Tac are excellent companies to do business with.

The large size of the leather backing helps to spread out the pressure from the gun, which makes them comfortable to wear.

However, you can cut some of the leather if you want.  Here's what I did to my Supertuck:

I agree with the other posters.  The size of the holster is what makes it comfortable.  I bought a Crossbreed a couple weeks ago and carry every time I leave the house now.  No problems concealing my SW9VE with a T-Shirt and shorts.  For the belt, I just picked up a thick pretty still Levis belt.  Working well for me so far.

There is an option when ordering to have the "combat cut" I think it's called.  Basically the same trimming you've done.  I have one with and one without.