Common SAE grades are SAE2 (uncommon,) SAE5, SAE8, and SAE L9 (rare!)
ISO property classes are a decimal number - 4.8, 9.8, 10.8, and 12.9 are common (I don't recall the specifics offhand, I'd have to look them up.)
Those are the primary mechanical grades - there are also ASTM grades, used in structural applications, and I do believe there's one or two ASTM grades that exceed SAE8 in relative strength (and possibly one exceeding SAE L9.)
Once you get into "superalloys" (like ARP,) all bets are off. SAE, ISO, and ASTM grades only apply to standard carbon steel fasteners - they don't even apply to CRES (Corrosion REsistant Steel, or "Stainless." Stainless is/was trademarked, CRES is not.)
I'm trying to assemble a listing of OEM fastener sizes and notes on my site in the Tech section - start at
www.kelleyswip.com/tech.html, and go from there. If you find something I don't have, I'd appreciate the information!