As I said in your other thread, you're not going to be stressing that processor at stock hardly at all. You might get 10%-15% usage. Honestly, the 3570k is overkill. You shouldn't need to overclock those processors; especially for an office system. Run stock speeds to maintain longevity.
Or drop down to an i3 / pentium... there's a reason they sell those processors. People are interested in them since they work just fine for office PCs. You'll notice very little difference between them and an i5.
You don't need even close to 16 GB ram - even 8 is overkill for what you want. Just get 8gb of 1600MHz Cas9.
Get a 7750 for those computers that ARE connected to three monitors - the others are fine on integrated graphics.
frsty I honestly don't understand why you're even contemplating an i5 processor, in fact, I'm not even clear why you're willing to pay the Intel prices for mere browser and Office program usage. You could (and should) go for an AMD platform here because the value (needs/cost/performance) is so much better for your situation. You'd even be 100% fine with a good dual-core CPU.
I assure you that even with all those tabs open, and a few Excel docs along with a couple of Word docs open your processor will be in "idle" mode 90% of the time, that's how efficient modern (~last 3 years) CPUs are. Anyways, any i5 would be an extreme overkill for your needs.
And seriously, 16GB of memory? 4 would be sufficient in your case, 8 would be the max I'd even consider. 12 and 16 would just be semi-comical...and not in a funny way, if that makes any sense.