The GTX 950 is about to come out, the 850 came out last year.
The 750m was a great deal in 2013. Not worth buying today though. That's my honest opinion I'm sure people who bought a rMBP with a 750m recently will disagree with me.
Haswell is also 2013 tech, Skylake is supposedly coming in June and is not affected by the delays that have kept Broadwell out of 2014 on the high end notebooks.
In my opinion buying a rMBP right now is just like throwing money down the drain. Extremely overpriced compared to the competition and very outdated in the CPU and GPU department. Also there are 4K notebooks in 15" sizes shipping now the 2880x1800 the rMBP has is also old hat at this point.
Again I'm sure people will disagree this is just my opinion take it as you will but paying $2K on two year old technology is not my idea of a good deal.