I like a little castor oil(blend) as well. When I started RC the club I was in used 10%. I followed along happily and everything I had ran just fine on 10%. In my present club they mostly use 15% and so did I and every thing ran just fine again. Then fuel prices increased so I switched back to 10%.
Not much difference IMHO. But sometimes it is nice to borrow or lend a buddy a tank of fuel and if you use what "the gang" uses its kind of nice.