How "long" a fight lasts in a turn-based-combat system ENTIRELY depends on how quickly the player bothers with spending their turns. Being more strategic, and no time limit being placed on the paused time between turns, there's never any rush, and MANY times I would delay a big firefight by leaving to grab a bite to eat... or take a much-needed, tension-relieving shit... or something else I just had to take care of. So these weren't really "long" firefights because they were so drawn out, but because I took my sweet time.
The better I've gotten at the games, the shorter ANY combat sequences tend to be. The 1-5 enemy sequences tend to last 2 minutes, tops, but more like 30 seconds. The battles with upwards of 10 tend to last 5 minutes, max. The opportunity to choose my battles and go in with a decked-out crew and my own ability to absolutely eviscerate opponents with deadly aimed shots just makes the fights piss-easy. Of course, I don't START the game decked out or with a crew or with the necessary Skills/Perks to be ABLE to do this, so there are fights where I have to run away, or I lose and die and have to reload an older save before the encounter or flubbed line of dialog that pissed the wrong person off. But these were ALSO short encounters... because I died.
So I can't really think of any battles that lasted a long time because of the scale of the battle, and not because of me. Not in 1 and 2, anyway. I CAN think of single battles in FOT that lasted HOURS because of the massive fucking scale of the waves UPON WAVES UPON WAVES OF ENEMIES I had to fight off in a single battle, without break. But that's FOT, a game that REVOLVED around squad-based tactical combat, not role playing. Still, those battles were a lot of fun... if colossal headaches on Hardcore setting... ~_~