There really is no reason at all to go for the 450 if you are not running the Dakar. More power at the same weight like the 530 is a good thing in deep sand loaded with nav gear and fuel.
The 530/690 choice will come down to personal preference. For me it would be the EXC (in my case it's actually an SX-F with a modified EXC engine, 600cc
) for a few reasons:
- Weight: 25 or so kgs difference is A LOT.
- Simplicity: The KTM 690 EFI is far from 100% reliable, and fixing it by yourself out on the track is difficult when one of the many sensors, the injector or the fuel pump goes bust. The 39/41mm Keihin FCR-MX carb has been around forever and tuning is easy and well known. 95% of the bikes in the field will have it so you can always find spare parts (not that you are likely to need them).
- Lack of a back-up kick-starter on the 690: When you have an electrical problem that runs the battery down, you are screwed. Carrying a spare LiPo might be an option but if you don't know the cause of your problem you might just run out of juice on the second one as well. It sure is simpler to just kick it when needed.
It's true that the 690 engine will probably last longer overall, but it's not as easy to maintain for sure. Valve adjustments are not an issue on the EXCs, rarely needed on the XC4 or even the RFS engines once stainless valves are installed. Oil changes are also quick and can be done in less than 20 minutes.
If I were you I would also think about a low mileage late model RFS bike, like a 06 or 07 525. Very reliable engine (arguably even more so than the XC4) and you could put the money saved into some nice upgrades.