Well, I think this little experiment is over. I've been playing with my current party, and I find it a bit ineffective for IA. Mostly, because of three things (two of which were pointed out by Kerkes):
1. The effectiveness of swashbuckler drops dramatically during the course of the game. She was doing nothing, basically, in Underdark, except maybe for an occasional dispel of enemies' illusions or a fight with the sidekick goons. I figure she won't become more effective later on without fighters' HLAs. I guess, we'll have to wait for IA6, where swashbucklers will be improved by Sikret.
2. Lack of pure cleric. r/c is a really good tank, but having a 12-13 level cleric in Underdark doesn't really help. Some fights I find nearly undoable (I'll write an example a bit later).
3. Not enough magical firepower. f/m progresses in levels very slowly, and having a single sorc is not enough to handle all the magical stuff.
To summarize, this party is not as effective as I first considered. I am playing the Underdark part, and some battles are basically undoable for me. For example, I am stuck right now with Noble Djinni (Deirex' treasure cave). He's too tough to kill in melee (has anyone actually accomplished such a thing?), and I do not have enough magical power to kill him before he regenerates or finishes off my fighters (who might've hold on if only I had pure cleric with Greater Restoration on board). I won't even mention the battle with the Demon Knights in Demogorgon temple...
I guess, maybe I just not skilled enough to play with that kind of party yet, but well, as Sikret has written in IA's readme, one should draw a learning curve for himself. I find the current game a little too tough for my liking, which kind of takes out the fun, and what's the point of playing the game without having fun? So I'll drop this party for now and maybe start another one. Well, anyway, sorry if someone liked the idea of me writing the report, since, obviously, I won't be publishing it now. Not for that party, at least.