Thanks for the info/suggestions guys...plenty to think about!...just that the thought of eco, even UA eco+, is a bit depressing...so here's, broadly, my options...I think;
1. could use BD l/haul cheapies, and hope BD Gold u/g vouchers work ex-man and the full miles for w-fare are credited...have to get LHR Man tho, so bit of a hassle..
2. could go UA ex-lhr and get eco+ (*already* doing this in Jan tho, for a cheeky weekend in NY) and be sure of extra comfort and double miles..damn jet lag tho..
3. could do AC to Canada very cheap (hey, thanks v. much for the sample itinerary) but it's all eco standard..and jet lag..double ouch..
4. could do two s/haul J class to, say Alicante/Palma, and suffer no jet lag but two trips..slightly higher cost - say 400 plays 300 GBP..
5. could do a multi-leg euro jaunt..

Gentlemen, your votes please - you will decide - probably!