Quick one,
I ride in NH and Maine, so temps down to 15 and up in the summer.,
I have #2 500HO 2020's and a 2019 cf600. 
In the manual it says 5-40SG?, but my dealer will use the 15-40spectro as that's what he reps.
I called shell Rotella, and they said  the T6 5-40W synthetic would be fine as I have a "wet" clutch?  and this product does NOT have any modifiers which will mess up a wet clutch system i guess..
My head is spinning with the brands/types/ and cost as i have 3 to maintain so i would like to use the same in all 3.
Anyone's suggestions appreciated..   

In my cf moto 520/500s i use a 10w50 fully syntetic mc oil made for wetclutch (don't have one but the manual recomends it anyway) my dads also us the same oil in his cf c force 800 with wet clutch and it works fine.
(I use SBK racing 10w50)

Acording to the manual 10w.. is recomdendet down to -20c if it gous under -20c you should use 5w.. or 0w.. if it't realy cold.

You should use MC oil /for gasoline engines) in your machines

I would recomend 10w40 5w40 or 0w40. 15 farenheigt is about -10c so 10w40 or 5w40 would work fine, 15W40 sems more like summer oil when you don't do cold starts.
I always recomend fully syntetic oil even if the manual don't recomend it.