Well, I don’t know if this is of any help (as it might pre-date Hopes machine built wheels), but about 4 or 5 years ago I bought a pair of Hope factory build Stans 355 rimmed wheels from 18 Bikes, and one of the lads there checked and tweaked the tension – this pair of wheels were terrific, and indistinguishable from some nice hand built wheels that I’d also got. Following my experience with the Hope/355’s, I bought another pair from 18 with Flow rims. The latter were not tweaked & tensioned by the shop, and even with the Flow rims, the wheels did feel very slightly soft under load, and they went out of true within a couple of months – the guys at 18 bikes then checked and tensioned them, and hey presto, they were better than new!
As far as Mavic wheels go, I’ve been giving a pair of their Crossmax 29ers a good going over for the last year or so in the Dark Peak, and apart from the freehub needing slightly more servicing than something like a DT240, I’ve been very pleased with them. I’ve just returned from the Alps, where I did some very rough red and black DH runs and natural stuff – the bike is just a mid travel 29er trail bike, and I weigh about 13 stone in full gear, so the wheels took a right pounding, but came out completely unscathed (the tyres on the other hand;))