I saw that the latest seed of 10.8.4 addresses 'graphics drivers' (information available on Google), and I can be 95% certain that will address Retina issues. The 650M should be more than enough to power the display.
Anyway, I went ahead and ordered 2.4 GHz, 16GB RAM, 256 GB SSD rMBP last night. I spoke to a friend who has the 2.7 GHz model (paid the extra $120) who also owned the 2.3 GHz 2012 model. He said he did not notice a difference at all (he does exactly the same things for work as I do).
I suspect the only time you're really going to notice that much of a bump on processors like these is when you're doing a lengthy operation such as compiling video. Even on my current 13" MBP, compiling a large Xcode project takes less than 10 seconds. I decided, in the end, I could probably put the $120 to better use on some accessories for the MacBook, such as Magsafe 2 converter and a new case.
Thanks for all the help everyone.
I scored a new 2.4 8GB 256Gb 15" over easter for 10% off and 18 months interest free. Great machine you will love it. Glad i got the 15" and not the 13" . I don't even want to look at my 09 27" iMac.