5.2 His with the Polar 7.875 is an awesome combination in my experience. The deck really feels more like an 8.0 than anything narrower. Haven't measured it exactly, though. But that combination is really nice.
Edit: The Polar 8.125 is a very, very good shape as well. But I use 5.6 Hi's with that one, the 5.2s feel a tad narrow for my taste for that shape.
Caveat: I really only ride cast Ventures these days, so I can't really say about forged Vents as it's been ages since I rode any.
One more edit as I like talking about Polar and Ventures: despite the minimal width difference on paper, there's a big difference in the feel between the 7.875 and the 8.125. The former is below 32" in length with a short wb and has the feel of a true tech deck. The latter feels more like an ATV deck in my opinion. I ride the 8.125 everywhere from ledges to transition.