What affect does wrong level gear have?

[Delsus]

Delsus is sort of right.

When a piece of gear has an "Optimal Rank," you can wear it below that rank. However, if you're even one level below the Optimal Rank, you will not get the full benefit of the stats. (So it's not +/- 5 levels. It's just one level.)

I have never done testing on it, i just try to keep withing +/- 5 ranks of optimal if possible, but if you have done testing then your prolly right lol