I voted classic mode for dual aiming.
The iron sight mode is of course easier but then again should it be easier? If I have the ammo increase advantage of dual welding pistols then there should be a disadvantage as well. If you guys decide to keep the iron sight aiming mode then you might as well just have a single 9mm with an extended magazine because the second 9mm becomes completely irrelevant.
Perhaps you devs could make the iron sight aiming with dual pistols a perk for sharpshooter?
I think it's good as it is. The two aim styles are merely styles to best fit your personal preference, not one advantaged sight and one disadvantaged sight. The price you pay for double magazine size is the extra carry weight your incur from the second pistol.