Being a Diesel Mechanic here in Australia this is an intetesting topic and I believe the results are transferable
We have found folks that run low viscosity oils tend to build up more carbon in the exhaust manifold and on top of pistons
In the Rocket 3 I believe Triumph has got it right, it's pretty warm where I am and I would be running a full synthetic 15W 50
15 for easy starts and cold warm up and 50 for the gears and lower Maintenence in the long run
Also, it's a common misconception that you don't need to warm up your motor, the reasons for a good warm up is to get the oil up to tempiture so it can lubricant properly before you rev it to hard when it's cold
A 1 minute warm up period would be a minimum in my opinion, also on the other side a good thumping up to near redline at least once a fortnight to keep the motor running clean
