Wouldn't be better to use overcharged instead of rapid fire since the original ROF 4.5/s is pretty high to me?
That's the (old) big discussion in the outfitting subforum - OC vs. RF, with a side order of Double Shot.
In my opinion, the shortcoming of the pacs is their reload time - default is 5 seconds, OC doesn't change that. RF gives you a 1.75 second reload. Add Screening Shell on top, and OC sits at 2.5 seconds reload, RF at 0.88 seconds.
That reload time then shows up in the sustained DPS - I know that Coriolis isn't perfect, but it gives an indication: OC/SS gives you 82.4 SDPS, RF/SS sits at 120 SDPS. The downside is, of course, that RF will go through your ammo twice as fast.
The ROF itself is pretty much meaningless - you get three shots per reload, as fast as you can squeeze them off. The difference comes in when you need to wait 2.5 seconds for that reload or you have it in less than one second. For me - and that's highly subjective - this means that I can often squeeze off two salvoes per pass, instead of just one (taking into account that you need to get close). And if I can manage to get short distance broadside towards my opponent, it's pure slaughter.