Just for another opinion: I've used both a 44 tooth and a 43 tooth on my 09 V. Did not have to change chain length - simply re-adjusted. 43 tooth worked best for me, so I later put it on my 10 V. The 09 V speedometer agrees with my Garmin nuvi GPS. My 10 V is 2mph slower than the GPS. Both bikes show same GPS speed with same RPM, so the 10 V speedometer is 2MPH slower than my 09 V speedometer.
I didn't find any problem in installing the rear sprockets. And, several people on this Forum have reported difficulty getting the front sprocket-nut loose. So, INMHO, I recommend changing the rear sprocket.