Mobo bending

Will having the heavy NH D15 SE as my main cooler bend my motherboard? I want to get 5 years of life out of this PC and I feel that's very reasonable. But I'd like to not like a $300 mobo and whatever the cooler takes with it if it fails on my first attempt at air cooling. I survived the custom loop, now I'm dipping my feet into this.

It will be fine.

Unless you have the cheapest mobo on the market (@$300 you don't) it's a non-issue. This was a problem many years ago, but no so much anymore.

You will have three anchor points at the top of your MB. You will be fine.

I have run the NH-D14, the NH-D15 and the NH-D15S steadily for years. When I am not testing other heatsinks, I use the NH-D15. No problems.