At 1080p (and the knowledge that i'll be getting a 980ti in approx 18 months), would the extra grunt in the 780ti outweigh the new factor of the 970 (I'd be getting the ref cooler model from OCUK)?
Nope, the "extra grunt" between a reference 780ti and a factory overclocked GTX970 is so small it won't even be perceivable to the user at 1080p, if you're getting a 980ti in 18 months then GTX970 all the way.
Yes the 780ti is £20 cheaper than the KFA2 on offer, but the 970 comes with a free game (which can be sold), an extra GB of VRAM, a quieter cooler, and will use less power while running cooler, it will also have higher resale value in 18 months due to not being a dust buster (the market for used cards that are noisy and power hungry isn't great).