As long as you have a way to scan get several pulleys. They are cheap, people are always putting them up for sale. I have a 3.4 with an Intense custom "canned" tune on my Gen III with mods in my sig and I see 0 KR. My plan is to start collecting pulleys from a 3.0 - 3.3 and start dropping until I see KR then I'll go the next size up. Every car is different and where you live plays a part to.
As for both pulleys "working". They will, but with each .1 pulley drop you gain ~7.5HP. Each degree of KR kills ~5hp sooooooooo.. for example...
3.4 pulley base line.
3.3 pulley 0 KR = +7.5hp
3.2 pulley 2*KR = -2.5hp from a 3.3 but 5hp over baseline AND possible damage... so you are getting more power from a pulley one size larger and being safe when it comes to KR, win win
Hope this makes sense, it's just tinkering with YOUR car to see what it likes best.
And as for the "pros vs cons" of a Gen V over a Gen III don't come into play until you drop below a 3.0 pulley anyway I believe. Now if you are intercooled, then that's a whole new world..
my $.02 so take it with a grain of salt. I could be off my rocker, I'm learning as I go... lol
