Cheers guys. Bike is in bits (that often doesn't end well with me but don't worry, I know how to get this far
). I went under the tank to check if I had a k&n (I don't, so will order one) and saw the ECU just sitting there...
ECU is now off and I spoke to Neil at cornerspeed this afternoon. Postal service is about £250, whereas BSD custom remap is £450. Honestly I don't think the cost is bad for either, but I'm not sure I can be bothered with the schlep of ~250 miles round trip, on uninspiring roads, in November, to eek out a small marginal difference of a custom map. Posting the ECU for 90-95% of the job and about half the price sounds appealing. Testimony from people here gives me comfort in the Cornerspeed option.
Problem is I was very happy with the BSD map on the S2R1000. I think I will order a k&n and while I wait decide whether to post the ECU or postpone the whole thing until spring and take it to BSD.