I'm always flipping tractors (to fund my other tractor restoration projects)......I use the T5 in almost everything,and T6 in my fourwheeler, whatever does not get T5 get triple T 15/40. In my experience the CAST IRON K series kohler engines seem to love the triple T. Newer "alloy" engines seem to work well with the T5.
That being said I recently switched over one of my JD's (JD 185, 17.5hp KAW.) to T5, the first 3 times I ran it I got a puff of smoke at startup. Smoke was a bit of fuel (you have to choke a KAW almost every first start even when warm outside) mixed with a bit of oil from what I could tell. Now it has quit this behavior.....I'm not sure what to make of it, should I go to triple T 15/40 or 10/30 ? Should I write it off as the oil cleaned the bottom ring really well and seeped while doing so.......
My thought was: The oil seeped after shutting the mower down HOT, this was my basis for the conventional heavier weight question....