I have both the KTM and the DRZ, and I have ridden the XR400 as well. If you're going to stay at 400cc, go with the DRZ. Sure, it's a few pounds heavier, but it's not noticeable and the e-start is worth it. In addition, it's probably the most dual-sport-able bike of the lot. It just runs and runs. If the weight is a problem, it's really about bottoming, and you can do cheap mods to your forks and shock that will do everything but make it a moto-crosser. Also, several members have suggested low cost ($3!) mods that really wake up the power, but I have yet to try them.
If you want KTM (which means you want a serious bike!), I would go 520. Same weight as the 400, loads more useable, tractable power, not much price difference. And I have run it for 100+ miles at a crack in the southern New Mexico desert in July without a problem, including both high-speed and technical runs; bike didn't even break a sweat.
All that said, I think it's pretty clear that the limitation of either bike is that your riding buddy is (or soon will be) on a TTR225. With the KTM, you will want to continuously leave her (or anyone else, for that matter) in the dust. The DRZ will still way outperform the TTR, but it's really the best alternative. Read all of the latest reviews in the last three months, and all of the mags have said the DRZ is the best trail bike in the world (stock), bar none.
Finally, no way I'd go with a KLX without major mods.
Hope this helps.