coming from a G4 notebook myself, I'm in the same situation as you. The only reason I want the 15" is for anti glare. I actually prefer the size of the 13" and wish it wasn't glossy but we have no choice.. and I don't care about the 15-20% increase in performance on the 15" because it will do little for me.
so today I decided that it's not worth spending an extra grand only for anti-glare, and I can live with glossy if it means that I save close to $900.. I get so much more power than my G4 packed into that small footprint of the 13", it has all the same ports as the 15" so you can always connect to an external monitor (which can be matte, so you have the best of both worlds).. It just makes a lot more sense.
anyways.. I ordered a thinkpad last week but now that I'm fine with the 13" glossy idea.. I'm thinking about canceling my order and going with the 13" MBP for myself. ahhh, too many decisions to make here..
haha i hear ya! too many decisions to make, ditch thinkpad and get MBP~!
External monitor sounds great. I'm just thinking about connecting it to TV when I'm at home with wireless keyboard and all. I like how 13" MBP has all the same ports as 15"