Having done 2 Kings Cross-Edinburgh returns recently, on the 2 stop fast services, have found the performance and time keeping to be good when they run to their pathing, with Kings Cross-York achieved in 103.41 mins last Mon 23rd Feb, on the 09.30 Kings Cross-Edinburgh and similar a few weeks earlier, then the 49 mins timing to Newcastle seems to be too tight as not achieve this timing yet, being about a minute within timing, then it gained back the time on to Edinburgh, arriving approx 2 mins early, so taking approx 4hrs 05 mins for whole run.
On both return runs, the trains struggled to keep to keep time, with the first suffering 5 mins delay near Drem then loosing time with freight train near Newcastle, then speed restriction around Peterborough, arriving Kings Crossvi 29 mins late, then second run, running well to time most of the way, till Grantham, and a Lincoln to King Cross service running 5 mins late, impeded us and we ended up about 4 mins late, so not bad, but it seems train struggle more Edinburgh-Kings Cross to keep to time than out of London.
I think the fast services are well pathed and seem to run to time pretty well, but as usual they are reliant on everything else around them running to time and not conflicting with them. I think the timetable overall is pretty decent and well executed.