Not based on personal experience, but I've been told that the 4K spring can tend to kill some bottom end power while adding more revs top end. This was from some pretty reliable sources so possibly you might want to research that part of it, and also look at where you need to make power? Of course the size/weight of the swap vehicle would have a lot to do with what kind of bottom end power/torque you need. Based on this info I decided on the 3200 rpm #366 spring.