Got sorted, bought set of German e-bay seller 18" (209 style - 5 spoke) with Goodyear Ultra for nudge over £600, tyres with 6-7mm tread.
Seller has these slightly cheaper ones (less tread on tyres) here:
http://www.ebay.co.uk/itm/Original-Bmw-X5-E70-255-55r18-Kit-Winter-Wheels-6mm-Top-/321608745550?pt=UK_CarParts_Acc_Wheels_tyres_Rims_Car_Wheels_ET&hash=item4ae160024e
Got two delivered yesterday and expecting other 2 on Monday - Wheels are as described and mint. Shipping is done by each wheel (own tracking nos etc, so not to alarmed that they are split up during delivery
As a side note I got a set of new 19" Bridgestone HP Sport RFlats from Oponeo:
255 50 19 Front @ £165e
285 45 19 Rear @ £186e
£702 in total which I thought was a good price, delivered 3 inside 48hrs and 4th one came the following day. Tyre's were manufactured in June & September 2014, so not old dusty stock but brand new. Dealer is going to put Bridgestone's on my new replacement wheels for me, as opposed to removing existing tyre and putting old tyre on new alloys.
Was going to see if my dealer would sell my alloys that are being replaced under warranty back to me, but apparently they go back to BMW UK for assessment / destruction / remanufacture (who knows).