I don’t know any sites besides maybe PC Part Picker, but you should be able to just check that the desktop you use as a benchmark has the same model of GPU and CPU as the one you want to buy.

You might have one with a GPU built by Asus vs another by NVidia itself, but if they’re both 3070’s then they’ll still be comparable.

Alternatively, if the one that’s been benchmarked has weaker hardware than what you want to buy, but still passes the test, then the one you want to buy will probably work. Typically weaker hardware has lower model numbers (3060 < 3070, 3600X < 5700, etc).