Hi, (I'm a uk member)
BMs are usually bulletproof.... usually. The smaller engines don't take the mileage as well as the larger 6s but are still pretty good.
As long as there is a FULL (preferably dealer) history with the car then 80k won't matter. If you think that the average annual UK mileage is about 12k and you'd probably want to ditch it after 3 year max, you are looking to put 40k on the clock.
120,000 is fine for a looked after bm.... but your resale value will be crap.
You might find that buying a more expensive one with less miles will get you your money back at the end of ownership.
Buy: 2yr old - £14k - 318 - 80,000 miles
Sell: 5yr old - £6k - 318 - 120,000 miles
Buy: 2yr old - £18k - 318 - 40,000 miles
Sell: 5yr old - £14k - 318 - 80,000 miles
Obviously this is a rough example but essentially it will have cost you less after 3 years because of the residual value.
Original question - I'd buy a BM wityh 80k on the clock with history and all the gadgets I wanted.... otherwise I'd wait for a minter.
<span style='color:blue'>"So my BM makes me a flash bastard? Then I guess you're just keeping it real from the seat of your nova?"</span>
<span style='color:gray'>"...and the home of the brave..... is bravey 130bhp from a 7 litre engine? 100bhp/litre or don't bother building it!"</span>
<span style='color:red'>"Aaahh the UK; where every road is jammed, under construction, poorly maintained and unfairly policed, at least we don't get over-taxed for it........ HA HA HA!"</span>