My question to the whole tactics/improved battle mods crowd is, why on Earth do y'all think they're fun? Challenging yes, unfair certainly, but fun? Hmm.
Back with the original Diablo variant community, we'd invent challenges by impairing the character in some way. To relate this to BG2, that'd be like making a party from a Transmuter PC, druid-spells-and-lycanthropy-only Cernd, conjuration-school-only Edwin, conjuration-school-only Kelsey, conjuration-school-only Jan, and no-magic Minsc. (And/or no-magic Valygar.) It's the Masculine Summoning Sickness party! :evil:
My point is, you don't need to install bokou mods to make the game more challenging. Setting personal limits and restrictions adds back in the difficulty sorely lacking in normal BG, and it's a lot of fun to boot. Anyone ever play BG2 without using metal items? A whole party of six only using clubs, quarterstaves, slings, and darts? C'mon now, don't everybody raise their hands all at once.
And to answer the original question, I had more problems with the Big Five in the Bridge District than any other fight in the game. Not even the oldest resident in the Docks District gave me as many problems as they did. In ToB, a certain somebody's son gave me 20+ reloads.