Going to level my rogue alt next. I have all pandaria treasure weapons, in this case 450ilvl (86lvl req) STR onehanders and one AGI dagger for offhand. I "enjoy" leveling combat spec, so is it reasonable to use STR weapon in MH?
It's just leveling, i know, but is pure AGI better than weapon dmg? Notice that it has no secondary stats. I also has Blade of the Prime, but it has even lesser STR and dodge.
General rule of thumb for combat through Cata was that a strength weapon one tier higher was superior to an agi weapon. Based on a quick glance at Shadowcraft, it appears to still be true. The difference between the 476 str epic heroic drop and the LFR Gara'kal isn't HUGE. It's only about a quarter of the upgrade that you get from going LFR to Normal Gara'kal.
The Yaungol Fire Carrier also has flipped Str and Stam stats, so it has a much closer to equivalent value in the primary stat department as well. The real problem with it is the COMPLETE lack of secondary stats. Your best bet is to check the price of Fist of Fate on your server, and invest on one of those if you can spare the coin. Since they're outside of the 80-84 twink bracket, I know on the servers I play on they're much cheaper than the 84 weapons.
Barring a Fist of Fate, which also has the upside of being usable at 85, the Blade of the Prime is probably your best bet. The Mastery is worth more than the extra strength (the proc from the Fire Carrier is bad). You probably won't upgrade the Blade until you get a 450 agi weapon (or 450 str weapon with 2 DPS secondaries).