Every year the numbers of 60's in traffic increases due to the 66's being used on the RHTT's. It used to happen with 37's too.
The numbers generally fluctuate between 5 and around 15 in traffic.
The 60's were the last main line type 5 built in the UK. Not sure about something larger being mooted, due to the downturn of traffice beginning to creep in at that point in time, and I doubt very much if the 60's could be adapted for passenger use - they were designed for one thing - digging deep and working on stuff 3,000 tons plus.
Saying that I have had them on tours, and they do OK. (but theyre not as fast as a 56.....!)
As any driver will tell you, once opened up on a sufficiently heavy train, they dig down, and compress their springs and you can feel it.
From memory their traction motors prohibit fast running, but I have heard a few stories of them being clocked in excess of 60mph. I dont think they take power off you and apply the brake as a 66 does though.