The difference in choice between the XT660X and the DRZ400 it's down to what you really need the bike for?
If it is just to keep it as a toy, and to go out to play with friends, then the DRZ wins it because it is a lot lighter, more of a fun bike, specially if wheelies and stoppies are what you're after.
The tank range of the DRZ (it only carries 7 litres) can be an issue when you realize the XT carries 15 litres of fuel of which 5 litres is reserve.
The DRZ has a great little engine but it needs frequent services and oil changes and failure to change the oil often will result in poor engine life and expensive breakdown / engine rebuild.
The XT is good to go for 6000 miles in between service due to it's capacity to carry 3.9 litres of oil in the frame.
Yes the XT is the heavier of the 2 but it has a much more powerful engine which makes the DRZ feel like a 125cc in comparison.
Speedwise the DRZ which is only 400cc, struggles to reach 90mph whereas the XT cruises at 90pmph and can reach 110mph unmodded. The XT is a reliable commuter and can handle herself up against bigger bikes.
But as I've said if commuting is not your game and you only need the bike to have fun for short rides then the DRZ is the ideal of the 2.
For more info on the XT bikes visit www.xt660.com
Good luck on your choice whatever it is.