Thanks for your reply , that was exactly the type of info I was looking for. I have no intention of trying  Nevis downhill black but think Glentress red is great except long uphill slog so will probably give new Nevis red a try before summer is out even tho it is a long way to travel for a days riding (from Airdrie) If so will post again in case anyone is in similar dilemma. I have a good quality hardtail (Trek 8500) and hope lack of rear suspension will not be a handicap , never found it a problem at Glentress.

In case I put anyone off Glentress black by my comments I gave up half way through initial long climb as it was over rougher terain than uphill sections of the red and I just was not enjoying it rather than feeling it was totally beyond me. Never persevered long enough to try downhill sections so can't comment