If you wanted higher accuracy but less damage, for say force of anguish, you'd probably just be better off using a spear/buckler combination, though I guess you'd get less wounds that way.
You lose a chunk of accuracy putting the shield on. Not from the shield accuracy penalty, obviously, because buckler doesn't have one, but from the bonus accuracy you get for wielding only a single 1h weapon. Fist+offhand is the same accuracy as single 1h and that's the highest you're going to get. It just has the added bug/feature of giving you dual wield damage on Full Attack abilities.
I don't know for certain whether you lose the two weapon style bonus, but I think you do.
@Josip: The consensus was (maybe still is) that fists aren't as good as weapons because no enchanting, but personally I think Climhazzard's numbers earlier in the thread show that it's at the very least not as clear cut and that fists have plenty going for them. I just don't know if plenty=enough. Even if the damage/accuracy bases skewed in favor of fists enough so that fists ended up being just as good as an average speed weapon with a lash enchant, you're still missing out on a possible slayer enchant for specific fights (if you do that kind of thing) as well as the baseline bonus all the weapon types have: accurate, DR bypass, dual damage types, etc. Five accuracy or 3 DR bypass are nothing to scoff at.
The problem of when to use high damage and when to use high speed is that, like Climhazzard mentioned above, monk fists are already fast weapons and already do damage equivalent to average speed weapons (discluding sabres). So I think you never use fast weapons unless you really need a secondary effect that one has. If you're not using fists and other secondary effects on weapons you can't enchant yourself aren't a concern, I think it has to be sabres or spears.
The usual downside to sabres is that they're slashing damage only, and that's the damage type with the largest number of npcs that have high DR against. But assuming you're running empty hands on swap, it's not a big deal for monks. The benefit to spears is that they're both Accurate and in the Peasant category. For solo, I'm planning to run a pair of spears in offhand (mostly for a secondary damage type vs crush resist mobs, since I can't get the drain spear) unless I can manage to get down far enough in Endless Paths to get the fireball sabre. I'd like Purgatory, too, but the only place I've seen someone mention it drops from is an early act 3 fight and when I did that fight I didn't get the sabre. Not sure if it's just random loot or what.
Edit @Josip re: above post
Spears are average speed.
Edited by Casildar, 14 April 2015 - 01:04 PM.