Why would you end up £300 out of pocket, he'll still have a GPU. Unfortunately we can't know for certain where the 560ti price will end up.
Two things will happen though, if the gk104 beats a stock 7970, a new 7970... or a new name like 7980 will be released with the clocks everyone can overclock to anyway, I'd be very surprised if the 7970 at 1100Mhz + was beaten by a GK104.
From everything leaked, nvidia is releasing a probably similarly sized core to the 7970, but whatever they call it 660/680 it will be the fastest Nvidia card you can buy for a while so will unlikely be priced very high.
Nvidia COULD do a crazy AMD like value launch, make the Gk104 like £225-250 and the GK110 £400 ish, that would really make AMD look bad. The general history of Nvidia is not to go the value route, but with low end disappearing market share winning strategy's could work for them in the mid/high end for a while so its possible. The more likely situation is a GK104 being ahead of a stock 7970, a GK104 overclocked being noticeably behind a overclocked 7970, being launched at £300 + and the Gk100 being £550+.
IF it comes out at £250 and the 7950 doesn't price adjust to match, I'll get one, if some competition and more likely the 7870/7850 release brings prices down, I'll see where they all end up afterwards. My guess is 7950 overclocked will also be ahead of a gk104, but priced a little above.
As for Nvidia being underwhelmed, full agree with the stock speed on the 7970, at stock it looks woeful.
But when 99.9% of gpu releases the high end barely does 10% overclock on the stock heatsink and the 7970 does 30%+, you have to see the difference.
http://www.hardocp.com/article/2012/01/09/amd_radeon_hd_7970_overclocking_performance_review/5
72%, 49%, 48% faster than an OVERCLOCKED 580gtx. I don't know what overclocks 580gtx "do" on average on a reference heatsink, I'd be surprised if there wasn't more in the tank on that MSI card, but I'd be surprised if a stock cooled card got anymore than 5% more than that card gets.
Stock the 7970 is a dog, unleashed, its basically every bit as fast as the 5870 was over the previous gen.