Only two choices really (you gotta hit 428~ fsb to get 3ghz) the P965 chipset or the 650i. P965 if ya wanting crossfire and 650i if ya wants SLi, either one should hit 428+ easily.
Also to note, is that the P965 will need decent ram (PC6400+) as the ram speed is linked to fsb. Whereas the 650i will pretty much be happy running any ram as it can run fsb+ram asynchronously.
Good P965 boards are the asus P5b deluxe (£100~), gigabyte DS3/4 (£100~) and for the 650i board it'll be the asus P5N-e SLi (£77~).
Your best option in that price range for clocking is the P5B Deluxe if you've found one at a good price. I think you should definitely hop on that deal and snatch it up.
I loved my 975X mobo, but don't know if any sell for cheap or if you plan on upgrading to SLI/Vista etc... In any case, I would recommend the 650i mobo from Asus, inexpensive and looked solid, and I believe it was Ham that gave it a good review.
So where are you hoping to pick up the deluxe for £96, if it's that price then I'd be interested in getting 1, have looked here in the UK and most places want £120+