they are almost the same, assuming you gear them the same. the engines are almost the same. the xr600R i think has more factory ponies, but the xr650l can be uncorked to equal it, and has more torque.
the main differnces are. XRR has kick start only, XRL is push button only.
xrl has more stator output for accessories stock. but the XRR can get a stator upgrade.
all in all it comes out in a wash.
with routine maintnance, both are reliable engines. no differences there.
i think the main thing you will figure out , is that the older XRR's are getting harder to find., the XRL's may cost more now, but they are easier to come by. and alot of them have low miles, and mostly street miles.
now if you want to go big, get the xr650 R. thats a different ball game from what i understand.
1994 XR600R dual sport