No pump that I've seen used for watercooling is going to bend over these fins. Maybe if your pump's pushing a couple hundred psi you should worry.
Even the 0.016" fins that I made were plenty stiff. Remember that they're only 0.150" tall, so they're not flimsy at all. If you have a feeler gage, take a look at 0.015" and 0.030". Even though the materials are different (steel vs. copper) you'll get some idea of how stiff they really are.