what is the XTZ reliability like and handling/power compared with other yamaha big trailies like the 660 and 600 tener?

don't know wheather to try one, it's got to be OK for a 2 up trip from UK to south africa, I'm not mechanically minded so needs to have a reliability record like a BMW

Hi,
comparing XTZ 750 vs. XTZ 660 ? Well, XTZ 750 has much more powerful engine than singl tenere, and that is the only one advantage!
Handling, fuel consumption, reliability, autonomia and everything else is better on XTZ 660, that is my expirience. If you are planing to ride with pasanger and are keen speeding on straight sectiones maybe 750 is better chanse, but I guess that are not important for overlanding trip. Comfort is almost the same. Count that 750 is well known huge fuel consumption bike, so choose....
Regards,
AnteK

Although I've never owned one, I've always heard that the 750 seat was very uncomfortable.

The engine is similar to that of a TDM i.e. shim under bucket with possibly a five valve head (FZR1000 technology) i.e. cams out should valves need adjusting. Not for the inexperienced home mechanic.

I've also heard that the gearbox is not the best, a la early TDM's.

I have seen some XTZ's fitted with the later TDM850 engine with the 270 degree firing order that mimics a 90 degree v-twin, which should provide better traction and the added bonus of a better gearbox.

As stated earlier, I've not owned one and I stand to be corrected but all of the above is true IMHO.

Steve