If you want a system that's great for pirates, musketeers, and the buckling of swashes in general, I strongly encourage you to take a look at 7th Sea.
I have, but for realistic, detailed fencing, great tactical depth (die pool allocation and maneuvers), and smooth play, I find TROS can't be beat.
Incidentally, TROS is also my first pick for historical Japanese games centering on samurai, even over Sengoku (although I'd probably use it for a setting book, just dumping out the rules/mechanics). The combat system is great for it, and the Stealing Initiative mechanics cover Iaijutsu nicely.
The funny thing is, while I want to run a Conan game in TROS, it's actually the one I think will fit the system the least (not badly, though), despite the game's name and sword & sorcery inspirations, and the general harsh realism of Howard's novels (sure, Conan is awesome, but he can't cut through mail hauberks and he can't fight ten men at once unless they're drugged-up degenerates who don't know what they're doing, à la The Slithering Shadow). Conan d20
actually captures the action and feel of Conan pretty damn well.
Intertesting thought here - this might work. The thing is to make toughness have an effect to a point, but not overly to much of a effect. I like the TN idea, maybe a minimum would level of one? Perhaps combining this with the reduced shock for toughness, or using it as is. Only thing is that it requires an extra die roll, but TROS can actually be played rather quickly for all it's detail.
The other thing I had a problem with was the wounds that would be caused by a +3 damage weapon vs say a 0 damage bonus weapon. That TN thing might work for this too. Don't get we wrong - A battle axe can cause great wounds, but the standard arming sword can too, and a +3 wound level seems too severe.
The Companion actually recommends a lot of "change it into a die pool" fixes for combat; frankly, the core book by itself feels VERY incomplete after you've read The Companion. I think the combination of damage die pool and Toughness TN works great to mitigate the main issues. It's also already a part of the game's mechanics - "use your opponent's attribute for TN" is everywhere in the rules (such as in Stealing Initiative).
And while it does add another roll, that's only "up to par" (RuneQuest, for instance, has three rolls per attack, and so do most other games I've played). I found TROS combat to be so surprisingly fast and smooth I wouldn't worry about adding a damage roll. (The main delay is players picking maneuvers, which should go away with experience; not that mine lingered long on the choices on their first time, even when using the TFOB grappling rules.)
Dangit, but now I want to run The Riddle of Hârn.
Edit: Funny thing, that made me think "but the combat is very Renaissance longsword." But then I realized that's just the Winding & Binding mechanic (optional, from TFOB) and some of the combat styles and maneuvers (like longsword). You can't half-sword with Sword & Shield, and the game even supports things like striking at a shield user's legs as a good tactic, etc. It should work great for more 11th-12th century combat, too.