Steam is adding a feature to add hardware specs to Steam reviews. This should make it easier to find reviews with similar rigs to your own, or parse when performance complaints are actually on the reviewer. As shared in the most recent Steam client beta patch notes, Valve has "Added the option to attach hardware specs when writing or updating a Steam User Review on a game's store page."
This new option should make it much easier to guess why one may be having performance issues, or to estimate how your rig should perform relative to others. Naturally, it will only give users the option, and reviewers could still choose not to share their specs. Steam also doesn't share how (or if) it will be verifying those hardware specs. Though, presumably, the best way will be to search your system specs the same way it does for the Hardware Survey.