The 690 can do highway speeds easily and I always ride mine 30-40 miles minimum just to get to the dirt roads and trails. I am only on the highway for at most 20 miles at a stretch and would not want to just drone along for hours on the 690. I have a KTM 990 Supermoto R and love it but would not want to do much dirt on it. It could do smooth dirt roads OK but the 17 inch wheels hit potholes much harder and the cast wheels could bend if you hit something really hard. Same for the Hyermotard. On the other hand the 690 is built very tough so you can beat the hell out of it and it just yawns. The 690 needs a more comfy seat though as the stocker is a torture rack. Also a small screen does wonders at highway speeds. Either of these bikes will seem crazy fast compared to your 350.
2009 KTM 690r Enduro in da house
2002 RC51 SOLD
2010 KTM 990 Supermoto R