I had the same decision to make a few months ago and went with the 1070 --- I certainly can't fault it so far. There was something very appealing about the 970/7075 combo but after factoring in another $50-$100 for cables the price differential was just too great without having any real idea of how noticable the sound quality would be (although the warranty is a bit better). Now, if the 970/7075 combo was say $1149 with cables thrown in I probably would have went for it --- for an extra $250 I would have gambled, but for $500 I folded.
Another factor I tried to consider was resale value. I could be totally off the mark here, but I think the 1070 will retain its' value better than either the 970 or 7075. A search will show that current asking prices for for the 950 prepro is not much more than the asking price for the 1050 receiver but the original price of the 950 was significantly more. As for the 7075, well to be honest, if I were picking up an amplifier as a step up from a receiver I'd probably go for an amp with double the rated power of my receiver, whether I really needed it or not. If you're looking at keeping your purchase for the long term though this may not be an issue.
If you're seriously considering the 990 though, I have no doubt the sound quality will be a noticable improvement over the 970/1070.