This will be a long answer. If it's too long for some, sorry....
Where you put it on my scale of flight model goodness :
Freelancer (terrible)
X-com interceptor (bad)
X-wing alliance (average)
Freespace 2 (above average)
Elite Dangerous (BDSSE)
I haven't played the first 2 at all. I did play Xwing around '94-95 (was that Alliance?), and the Freespace series. I also played a lot of F18 Hornet online, Warbird, and a bit of Falcon 3. Of course I've played a lot of Elite.
It's hard for me to make a direct comparison; here's why: In the old days, I had a full HOTAS + pedals, so I had full controls on every axis. Currently I'm lacking pedals, so in Elite I have to Yaw with a hat controller. In SC, I roll with the hat controller. Why the difference? Because Yaw is very weak in Elite compared to SC. Not a criticism, just a fact. Since I can point the ship left/right more quickly with Yaw in SC, that's how I do it.
If I had pedals, I suspect I'd put Yaw in the pedals and keep Roll on the stick (the Elite method). But simply on/off control of Yaw in SC lacks precision, so I have to compromise.
But to answer your direct question: SC 2.6 feels a lot like Freespace and Xwing to me.
That sounds cool. Was it in AC, or the PU?
Both, but mainly in AC because there's no credit loss/insurance in AC. So you're more free to practice without having to worry about your losses.
Was it spontaneous parry and riposte stuff, or were you trying out different ships and loadouts against agreed opponents?
Both. So far, I've only flown the Mustang and Hornet extensively. I have some friends with other ships I'd like to try, I'm sure that will happen as well.
Not often, and only for a small durations... just as I do in Elite.
If so, does it give a much greater degree of maneuvering?
It does, but it's more movement than I like. I'm simply not great at highspeed-random-vector-floating and aiming weapons at the same time, whether it's SC or Elite.

I prefer the atmospheric type of flight model. I've heard that decoupled gave even MORE "greater degrees of movement" in 2.5, but I'm not good enough with it to give the best feedback on it.
I read the other day that contrary to the "everything is slower" vibe, some ships are now considerably faster in a straight line. That has led to all the racing module records being smashed since 2.6 launched?
I'll answer this backwards.
In essence, afterburner has gotten a lot faster. It's also directly tied with fuel consumption so you can't burn forever. So some ships can go 800 mph (or whatever), but not all the time. And not along a curving path (when you deviate your path, the ship begins to slow from AB speeds.) So for racing, yes - records broken. (Racing really isn't my thing yet. I usually get just lost on the course, even flying slower than a sloth.)
2.6 is Slower: well, yes. But here's how.
In 2.5, everyone in combat was flying around at 600 MPH. There weren't many turning battles, because you could easily engage at 2000 meters and stay there. Imagine if you were in Elite, and ALWAYS fighting a ship that was just a pinpoint target. It was sort of like that. You couldn't really have close turning-style battles, because at such highspeeds, the target would fly by and be 1800M behind you before you could even blink.
Personally, I didn't find it that fun. Had nothing to do with my skills, I just thought it was weird.
So 2.6 slowed base ship speed down to the 150-200 mph range. The result is much closer-quarter combat. Turn battles are now key to winning. You can still afterburn in and out of a fight, but it's like Boost in Elite - it's a strategic move. 2.5 was like chasing a housefly with a laser pointer. 2.6 actually feels like proper space combat.
Final Factor on Speed: When you're reading complaints from SC players, you have to keep in mind 2 other factors.
- People using Mice, and people using a Joystick. Just as in Elite, each type of player has a different desire. I'm a stick guy, and don't care if a flight model is impossible for mouse users. Really, I don't care at all. If you can't fly with your mouse, go play another game. I believe 2.6 favors stick users... or at least, heavily removes any sort of advantages (intended or not) that mouse users had. Mouse users can no longer sit 2000 meters away from a target, and use their pointer/gimbals to just snipe things as they float in random directions at insane speeds. I saw a poll last night on the SC forums; 67% of respondents said they prefer the 2.6 model. (I didn't read the 27 pages of 'why').
- People using Gimbals vs Fixed: Slow down the ship, and suddenly Joystick pilots using Fixed are now easily keeping up with mouse users with Gimbals. (Remember how Elite CMDRs are complaining about upcoming gimbal nerfs?)
So - when people are complaining about 2.6 flight, it's not just about "how the ship feels." It's about how well they are doing in COMBAT, and there are many other factors in combat besides the flight model. How well you aim, what weapons you use, what controller you use. It's layers of an onion.
I think CIG is attempting to refine combat starting with the flight model, and will adjust the other layers as well. What I've seen so far tells me they are doing the right thing.