Some are more slippery than others. The Brummel should be modified to finish in a bury for strength, then it will be as strong as the bury. I've been doing some work with Amsteel (Dyneema) and using the modified Brummel as detailed here. http://www.colligomarine.com/docs/misc/splicing_instructions_for_web_rev_1_2.pdf

Samson Rope recommends the bury (finished with a lock stitch) and has instructions on their site. Both of these resources emphasize the importance of a gradual taper for strength, otherwise the internal bump causes a stress riser that will be the point of breakage. Also for slippery line like Dyneema they recommend the length of the bury be 72-times the line diameter. Either splice if done properly should be pretty close to 90% of the line strength.