Honestly, the two seemed to perform pretty similar. But its hard to give an accurate comparison cause my first race w/ the B5 was also my first time at a new track. The track was really slick, where my usual track is a little more grippy. I like both engines. The only difference I did notice so far was that the mid range on the B5 seems to come in a little stronger than the +4.
I plan on trying both engines during the practice day at the AMS. I'll try to give you some better feedback then.