A higher injection pressure will always equal better atomization. This in turn equals better mileage, more HP and cleaner/more complete burn (less smoke).
I'll disagree.
My truck with 250/200's passes emissions tests with the EXACT same opacity numbers as bone stock tuning/injectors. Except it makes far more HP, gets the same fuel economy, and runs at much lower EGT's.
And I'll make far less smoke at 325 hp than bone stock injectors with their higher injection pressure and better atomization.
In fact, I'll make far less smoke at 400 hp than bone stock injectors at 325hp.
Point is higher IP doesn't mean better in all scenarios. It depends on WHERE in the power spectrum of an injector's capability you are running.
It's far too often that someone wants to make "X" hp, and the recommendations come pouring in for an injector, HPOP, turbo, whatever combo that will just barely get you there. Problem is that just barely getting there leaves you with a lot of power that is unusable for anything other than a very short burst. And when you do hit that peak that it can possibly make, you're running with a ton of smoke and EGT's that rival a thermonuclear meltdown.
Instead, get a combination that will supply MORE than what your goal is, and then tune specifically to reach ONLY your goal. You'll be surprised at how much more power you can use on a daily basis this way.
And with correct tuning, you'll be surprised at how good it runs. But that's the trick, getting the correct tuning. Still so many tunes out there that just can't dial injectors in properly to run streetable.