It's actually £18 more expensive to get the OEM + Cooler
However seeing the cooler getting fit it seems rather straight forward, I will make my decision before buying it I guess, but the aftermarket cooler does seem to be a good choice for the future, whereas the stock is a good option for now.
There's no real drawbacks for either because I'd be spending the extra cash now or in a few months time.
But if my money isn't in tomorrow I'd have an extra week to dwell on it, but then I'd have a GPU and screen sitting next to me doing nothing -_-

I've had ram next to me for a week, and a gpu will be next to me for at least 3 more days xD