Hoping to be out but can't confirm until Wednesday. If I can make it I don't mind leading a ride and doing my usual evening route (25 or 30 mile option), probably won't get around to doing a GPX though...
Don't think Belmont as an evening ride is worth it really, like you say we'd probably have to drive so a bit pointless and traffic will probably still be pretty busy at that time anyhow.
Probably better to find a decent North Bristol climb and have our own challenge, off the top of my head if you combine the lower and upper Tockington climbs that should give a fairly long climb, but you need to cross a junction in the middle which could throw times out (although it's usually quiet).