Do you reckon it will fit ok strapped to the top of a rack? or is it best split down and carried in panniers? I'm wondering if I can get away with just the two rear panniers with the tent on top.
*has a try*
In its compression sack, but not especially well compressed (not that it matters, the important dimension is the length of the poles), it'll sit on the rack of my DF tourer
[1] lengthwise and overhang by about 15cm at the rear, or horizontally across two panniers without looking daft. If you did something clever with the poles you could probably compress the rest of it down to an even more rack-friendly shape.
My general preference is to stuff it into the bottom of a pannier (with the poles and pegs in with the bedding, for better weight distribution), but I'm a 4-pannier kind of gal. If you're happy with all the weight on the rear of the bike, there's no reason two-panniers-and-tent-on-top won't work.
[1] This configuration doesn't work so well on the SMGT because of the angle of the top of the seat, but it would still go across the panniers okay.