Campagnolo 8, 9 and 10s levers up to 2009 used 5mm gear outer, UltraShift and PowerShift use 4.5mm gear outer.

Later UltraShift levers (late 2010 on) and all the PowerShift levers have a slightly differently-shaped and more open cable port to allow quicker, easier insertion of the 4.5 mm outer but won't take the 5 mm.

OK, I'm biased, but I'd just use Campag cables. OK, they are costlier than some other alternatives but they are 100% guaranteed to work if correctly assembled, they are long-lasting and the gear cable inners, particularly, are very smooth, supple stainless which runs freely in the correct outers without the need for lubrication and they suffer fraying at the head far less than some of the lower-cost alternatives.

I've assembled systems using Nokon in the past and still do so where required - I've had good results with that but generally only feel the need to do so in cable routing situations where there are tight bends to be negotiated - older Cervelo R3s for example used to place the d/t cable stops very close behind the head tube and getting either Campag or Shimano outer to bend as tightly as required was never a great idea and Nokon was a good fix for that.

HTH
Graeme