For years, many of the guys over at CafeHusky have been using Mobile 1, based on the recommendation of guys from ZipTy Racing.  ZT is recommending the 0-40, even for my wife's 310 where the manual calls for 15-50. 

I've not heard anyone complain or post an oil related problem where they are using the Mobile 1 0-40.  I'm using it in both my 511 and her 310.  The 0-40 is called the European Auto formula or something like that.  I buy it at Walmart for about $23 for a five quart jug.  There have been no clutch issues whatsoever - NONE.  Our gearboxes / clutches are smooth as silk and very easy to feather.

ZT also recommends a stainless steel mesh oil filter as it filters better than paper and flows more oil with less restriction.

Consequently, I'm not a believer in $20 a quart oil - I'll use 0-40 or 10-50 Mobile 1 in my/our new 690's at the first oil change.

Good luck.  Be Brave!