In reply to Neil Williams:
> I might be unusual in this, but I do enjoy a well-set 4+,
Where are you climbing, I don't think I've ever climbed a well set 4+! It's all ladders around here at that grade...
In response to the OP, I guess you just have to do whatever you need to in order to remove the frustration, I don't find it's ever particularly helpful to be foaming at the mouth when climbing. Probably get on some soft routes and maybe do laps for a bit of mileage, play a game like add-one or silent feet, or just go down the pub and have a beer, strike it off as a bad day and don't worry about it too much.
That said, I don't take my own advice in the slightest, I get really annoyed when I have a bad day and usually cut the session a bit short and then grumble about it until I have a decent session that lets me forget about the bad one!