Disclaimer!!! I own and love my XR650R and L models.
The 400 is an excellent bike but slightly smaller than the 650. At your height, the 650 might be more to your liking but then either bike can get higher bars etc.
But I suspect the XR400 would be better for "putt"ing around. The XR650R tends to overheat if you go too slow. Can be helped by various things but it will still get hot. Evans Coolant solved most of my problems with over heating on the XR650R... but that was only a problem when on REALLY tight trails.
If jetted right it will never overheat no matter what.
GET THE 650R OR YOU WILL BE CONSIDERED AN L7