I wouldn't use Gr 2 on anything I cared about.
They are noticeably weaker than Gr 5 & there is not much of a price difference. Having said that. a gr 2 nut is better than a gr 2 bolt.
The counter guys at Fastenal have some discretion on which discount multiplier to use so it is worth making friends with them & talk about what you are doing. Especially if you have an account set up so you don't have to do that every time you order. They also prefer lots of some qty rather than onesees/twosees