Not to keep beating this dead horse, but my opinion.
As I haven't ridden my BA in months but only my Thruxton, my viewpoint will be a bit different. First of all, keep in mind that the Thruxton on average, runs around 40 degrees warmer than the BA. Riding highway on a normal 80 degree day, it sticks at 215-225, where the BA will run at 175-185. Note that these temperatures are taken with the exact same temp gauge (I switch it between my 2 bikes). And when I used to ride every day in NYC, I'd see the temp hit 250-260 EVERY afternoon riding home.
So knowing this, I'd NEVER use the 5-40 in the summer. Now that the temperature has been in the 30's almost every morning, I did notice my bike refusing to idle properly. So I went ahead and tried the Rotella 5-40 this weekend, and have noticed drastic improvements with the ease of idle.
So I plan on running the Rotella all winter, then swapping back out for Amsoil 20-50 as soon as spring breaks.
