Thank you Gents. Love the pragmatic advice Jazz - many things are a compromise of two contradictory ideas. I'm getting the feeling it's ambitious from reading other build/use/buy threads - but if I can't spec it to do the potential jobs, I'll never be satisfied. When my noodle is approaching fry off temperature I'll be on here, asking stuff. The timescale is the tricky one - it's normal for me to end up taking years on projects, but with an analytical eye, rather than a doing hand (which I'm trying to change), it usually ends up right first time. ...there you go, I've gone and walked right into the trap - well, you laid the bloody gauntlet, I just had to pick it up didn't I. :-)