DR-Z400SM with a second set of dirt wheels.
The 650 is a pig compared to the 400. There isn't much of a power difference if you jet the carb properly, 3x3 mod, and throw a pipe on the 400. It is MUCH easier to find dirt rims(400S/E model) for a 400SM than finding Supermoto wheels for a 400S/E or 650. The 400 is better offroad thanks to the weight savings. Both are deadly reliable. I had 49,000km on my 400SM when I sold it.
Lets be fair, a modded DRZ is close to a stock DR power wise yes...but throw a pumper and exhaust on the DR and there is a big difference. And this can be done cheaper than the $1400 price difference on a DR and DRZSM. Yes the DR is heavier and since its year of the Pig I guess thats a good enough description
That being said here are my findings, and this is for me, YMMD.
I am old and worn out, of fickle mind and permanently cranky. I also have a 30" inseam. I don't care about beating other people on off road rides, jumping higher or hurting myself. I have been known to roost others tho. In the last 15 years , I have had 5 DR650's, 3 DRZ400's, 2 WR250's, a CRF250l, a KLR650, a CRF230SM (with knobbies) As well as a couple VSTROM 650's, a couple CB500x's, and more street bikes.
Take the spring Bethany (off road)ride as a test bed. The DR, Z, WR were all perfectly capable bikes for this. The Vstrom which I stupidly did, proved to be quite heavy and tiring but I made it through. The CRF250 was the easiest, mainly because of the engine and weight. You can lug the motor, unlike the WR. The little 230 was a laugh, its so light and flickable. i did have to lift it over some logs because of the 17" tires.
Step back and decide what your realistic expectations are. If you want to go fast, KTM. If you want to improve off road skills and never leave your county DRZ, WR, CRF. If you want to putter through trails, gravel roads and all of a sudden your riding mates announce a trip to Pennsylvania for backroad and gravel riding, or you want to visit your relatives in Ottawa (I'm in Toronto) the DR is a perfectly capable machine