Hi...from a happy 2008 XTR owner....and Welcome!

You sound very similar to me. When I first purchased my bike, I wanted MM 2to1 Exhaust...for the same reasons, plus the exhaust going under the bike did look a bit weird to me , then.

2to2 Exhaust do work better...plus you may get a warm leg/ engine with the MM 2to1 !

Also, my main worry was all the talk about Surging. Well, don't worry, and the 2009 model onwards has no serious problems/ ...hardly noticeable..have a butchers at this link....but Kev IS WORKING ON A MOD for your ECU anyway! (Kev is from Brisbane too!)

http://www.xt660.com/showthread.php?t=8546
and fuel..you should get 100 miles before reserve.....

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2008 XTR Mods : DNA Stage 3 Airbox, PC111, Carbon Cans Ovals, Steve Ruth built XTR734cc Big Bore with - High Desert Dyno (HDD)/ Cuervo Racing Gas Flowed / Ported Head fitted with +1mm Valves & uprated Springs, HDD 5050 Camshaft, HDD +3mm Throttle Body, CP 105.5mm 11:1 Piston, Custom Mapping, Piasini ECU, Renthal 613-01, Barkbusters VPS, Pivot Pegz, Touratech Bashplate, Foam Grips, Kev's O2 Sensor Mod, Kev's Extra Coolant Cooler, Wilbers Progressive Fork Springs and Rear Shock