RPM and rollout question/decision help?

[simplechamp]

Here's the deal: I have a Neu 1512/1.5Y/F (1850kv) that I was going to run in my buggy. On 4S it would be at about 27k RPM and I would gear for 40mph with a rollout of 1.6. Another guy offered to trade me my Neu for his Castle/Neu 2650kv. The 2650kv would be at about 39k RPM on 4S, I would need to put the 52T spur on my Slipperential and I could gear for 40mph with a rollout of 1.1

What would you do? I definitely need to stick with 4S. Is it better to have the higher kv higher RPM with a lower rollout, or lower kv lower RPM with a higher rollout?