I love all those bikes the RX, KLR650, and the Himalayan. I've ridden the RX3 and Himalayan, I wish I could take the RX and himalayan for an adventure ride.
I have not ridden the RX4 it has just kinda dropped off the radar for me. If you are around Azusa, California you can probably test ride one at CSC.
Remember they don't sell the KLR650 anymore and the KLR650 is much bigger in my opinion at least the 2nd gen one is I have the 1st gen. Really the competition in this lightweight adventure category right now is:
Versys-X300
F310GS
Himalayan
RX3
RX4
The closest competitor I suppose is the Himalayan with it's 400cc motor but it's not that powerful a 400cc. The Himalayan makes 24HP and the RX4 makes 40HP! Big difference in power. Now I'll tell you my DR650 makes about 30HP and it's more than enough for adventure riding, but yeah it's a torque beast.
I think the deal breaker for me for the RX4 is how well it does the pavement, if it can cruise comfortably at about 70mph it'd be a winner. I remember the RX3 felt kind out of breath at freeway speeds. Your definitely going to have to be in the right gear.
The Chinese stuff just gets better and better! If you think about it's about half the price of the Tenere 700 that just came out, good value. You probably don't have to farkle out the bike as much also. But speaking of the Tenere 700 I love that CP2 engine I can't wait to ride one