Ash, I've just bought an xt660r for commuting a 60 mile round trip on A and B roads, and some that are smaller, and the bike is in it's element. At the moment, however, I am travelling from Wiltshire to North yorkshire (til I move) via the M1, M18, A1(M) etc and the bike doesn't like these roads as it's not what it's designed for (IMO). I travel at about 70-80mph on the motorways which is reasonable but I wouldn't fancy doing a sustained 90mph as both bike and rider will soon get tired. If you do a few motorway miles mixed in with A+B roads try a TDM900, good riding position, better weather protection and more grunt for 90mph+ riding.
Mind you, having said all that, the XT is a stonking bike......
Pete