I’m not suggesting that you shouldn’t do Glentress – Ft William – Torridon, but its not necessarily the most logical/efficient driving option from London.
(1) If you are coming from London to Scotland I assume you will come up the M6/M74 rather than the A/M1. Glentress is then on the east coast of the country whilst you are on the west. You will pass many good options in the Lakes on the way, and then some of the less well known of the 7stanes trail centres near to the M74.
(2) If you are in Glentress heading for Torridon, then Ft Bill is not on the route most people would take (Edinburgh, Forth Br, Inverness, being the ‘obvious’ route). The road to Inverness will take you through Aviemore and access to the Cairngorms.
Of course if you’ve got enough time and don’t mind spending as much time in a car as you do on the hill then there is no reason not to do them all.
If you come back from torridon, then do you want to break up the trip back too? That will be difficult as following torridon almost anything else is going to be an anticlimax.