T5 is hit & miss. I often come through mid evening 8-9 pm and it's not so bad. An hour either side of that and it can be nightmare.I had been warned that JFK was bad but I had no bother at all the couple of times I went through, must have been lucky. T5 at Heathrow has been absolutely shite every one of the hundreds of times I've been forced through there.
I've waltzed through SFO once in 20 minutes end to end but other times stood in queues almost back to the plane for 2 1/2 - 3 hours if a BA flight lands at the same time as a Virgin and Lufthansa.