FR7 - small ring 93 action, turned down bolt, straight gripped stock. Apparently less than 4000 made.
FR8 - large ring 98 action, straight bolt, pistol grip stock. Apparent production around 55000.
My preference based on a small sampling is the FR7, it is trimmer, has the turned down bolt, and the ones I have seen have had smoother actions than the FR8. And my FR7 feeds flatnosed bullets no problem.
As too the ammo question, who knows, things are safe, until they are not. Spain was not a member of NATO when these rifles were converted. I use 300 savage data in mine.
Both the Argentines and the Chileans ran ran 48000 psi in their 91's and 95's. I'd bet the Spaniards did the same. IIRC, 308 and NATO run around 60000 psi, if a rifle was strapped in a test bed, I'd bet it is safe, but my eyes and fingers are important to me. So I'll stick with the mild reloads.
Spanish arms got a bad reputation from the cheap pistols they were turning out and from reports of Paraguayan rifles blowing up (who knows what really happened there).
Talk about unsafe, AFAIK, the Americans made more unsafe rifles than anybody else.
It would be interesting to do an endurance test on a Spanish 93 in 7.62, unfortunately (or maybe fortunately) it is probably cost prohibitive.