All right, I did STF but I can't find what I'm looking for so I'm going to need a fresh thread for my quick question.

Here's the scenario. Two NCs, both level 4 with one upgrading to 5.

What is the upgrade that would be better to start next, second NC 5 or NC 6? NC 5 can be started immediately after the other finishes, NC 6 would require a bit of saving, maye a few days since several million would be spent on a non-NC upgrade in the meantime.

Thanks.