I uprated the spring (not the shock) on the rear as i am a fat git
I have had the suspension setup and usually both front and rear springs upgraded on several bikes, It has always made a noticable difference. The 749R had the best suspension I have experienced out of the box.
But I still needed to change the spring on the rear anyway, and the shim stack cost no more than it has cost me to change the front springs on other bikes
I probably did not need the shim stack upgrade for the forks, but it was not that expensive and I was told that it makes a big difference to the front suspension. I will post more feedback after I have taken it on track