King ISO / Stan's Arch - Spoke Size?

QBP Calculator says I need 260, 261, 262... crap.

from my calculator:
Front: 260(L)/261(R)
Rear: 261(L)/260(R)
DT Swiss tells you the same thing if you take 20 seconds to plug the numbers you provided into the calculator, which is not a surprise, since the math is very simple. +/- 1mm is not going to bust your build. going over 3-4mm, on the other hand, will definitely cause you problems.

Where do you plan on buying the spokes? My buddy who built my wheels recently used the spoke calculator from DT Swiss and came up with some numbers. I then went to my LBS and got the spokes in which they used QBP calculator and the numbers were slightly different on the right rear wheel. I went with the QBP and they were perfect. Basically I recommend going to the LBS and have them do the calculations for you and if they are wrong you can take it back. Pretty tough to do if you buy online and they turn out to be the wrong length. Good luck.

Haha, I am the LBS. I ordered according to the QBP calculator, I gonna try to just use the 260 and 261, we'll see if I have to use the 262's.

I would guess that both sizes will work fine if there are within a mm, just one would be a little more ideal than the other. I know a lot of LBS' here only stock them in even number lengths, I've never encountered a problem. That said, I order from Cambria Bike because they have wicked prices for spokes.