The recomendation is a pretty loose lock stitch (with three full stitches a side). I haven't destruction testing them, but I have made the first pass through the side of the bury at the eye, and going down two braids per stitch. So far I haven't had one start to pull, though I am just now starting to put them into regular service, so I will report back when I see any results.
Personally I just am not happy with my brummel splices since they always seem to be made too loose and start to separate pretty early on, though I have considered stitching them as well. It just seems a bit of over kill.