Hi there, saw this thread and thought I'd contribute.
I have an 08XTX which I believe has the same gubbins as the XTR.
True there are a few issues with the bike's running as standard.
First I installed DNA stage 1 and stage 2 and kev's fuel mod; this definately evened out the power delivery across the revs and made the lower revs much more usable.
The bike still had the open/closed loop fuelling issue.
Next I replaced the ECU and wiring loom for and older version. (wiring loom �35 ebay and ECU about �110 from dealer.) ECU info
http://www.xt660.com/showthread.php?t=8546
This has totally smothed out the bike (even though I am using a butchered PCV map
Top half dyno generated before ECU change, Bottom half downloaded from site, copy and paste lol.
Kev has since released A device to do the same job as replacing the ECU,
http://www.xt660.com/showthread.php?t=14746 , but I see maybe they are no more. ?
http://www.xt660.com/showthread.php?t=14746&page=16
And a 10 min mod to the throttle grip changed throttle response.
Anyway just my input as my bike is definatly a very different ride to the bike I purchased as standard.