Rule6,
The Seca 750 is a beautiful bike, and nice sport touring ride. Have fun with that!
The KLR is much heavier than the KPX. Maybe swap roles once you get onto that build. Turn the 650 into more of a commuter, and set up the KPX for off road fun. I think the KPX will be much better. It is lighter, has more advanced features like the inverted forks, lighter frame and engine. It would be rewarding off road! The KLR has enough power to be a better road bike, and the extra weight will also help. Just an idea