Can you clarify exactly what you tested?
Umm :)... compiled and deployed on my test machine. Sure I haven't done any deep stress tests. IMO Kent pointed out somewhere in bcache list what's the best kernel regarding stability and mentioned 3.17 due some writeback fixes he made. Anyway, pesonally I'll be fine with 4.3.3 and can't wait for the official backport for my stumbling jessie. Thanks.