Why?
I literately just got my rMBP last week. 15". 16GB RAM, 256GB SSD, 2.8GHz i7.
I don't regret it.
I don't use anything that requires open CL and only game I play mobile are indie games and Dota 2. Nothing graphics demanding.
If the Iris Pro is the same performance as gaming, with superior Open CL, the 15" isn't a DO NOT BUY. It's a "BUY IF YOU NEED ONE, CAN'T WAIT FOR ONE, OR DON'T CARE ABOUT OPEN CL PERFORMANCE"
You'll probably not get the extra hour or so in battery life. Screen will be the same. Weight and shape will probably be the same. And you won't have the new fancy OS X installed.
You just spent a good deal of money on a notebook that's been out for over a year. Of course you're going to try to convince yourself that you won't regret it once the new notebooks are released.
See the little problem there?
To the OP: you're doing the right thing by waiting. Keep it up.