I thought a lot of the 2 pole motors took like 15 degrees and the 4 poles motors took 30 degrees. The bk is set a t 15 from factory.

From the factory, it is set on "Automatic". It should run fine if you set it at 5 degrees.

And 5 degrees will give me more top end?

It shouldn't do much. That is just a good amount of timing to start with. However, you could play around with the timing, up to 15 degrees, and check the motor temps along the way.