Hi John
Thanks for the suggestion of the Triopos RS3, the single lock doesn't worry me, but by the time you add a QR it takes it to something like the Pig Iron BH1V. I know some quoted weights are decidedly 'conservative' so for the spec I'd expect several of the 8kg quoted heads to manage much more.
As to the Sigmonster I've only had an initial play with it so far, but the results seem good. I've been hampered by the fact the only tripod I'd got that would support it was an ancient and very heavy Gitzo Studex 401(?) with a Rationelle 5 head which made it almost impractical to use! I've just acquired a Gitzo Mountaineer 3542 brand new for £399 off eBay! So with that and a Lensmaster Gimbal I can now start using it properly. The lens itself came from
MPB and cost £2699 so all in all the whole set up was pretty reasonable I think.