So my Pista came with a 1" threadless headset and I'm curious--is there any advantage to a 1-1/8" over a 1"?

-Chris

The advantage of 11/8 vs 1 I guess would be the larger diameter tubing, but the headset is the result of that change, there's no difference between the headsets themselves. In practice the real benefit is the greater availability of 11/8 stems and forks.

I would think that the only advantage is the larger, thicker, and therefore stiffer steerer tube. There is no real advantage as far as the headset goes.

I guess it makes sense for me to just upgrade to a nicer 1" when I'm ready then...

Well it would be impossible for you to upgrade to 1 1/8" as long as you keep your Pista, so...

You can't change sizes, anyway. You would have to buy a new frame with the proper size headtube.

well there are more balls to distribute the force in a 1+1/8, so in theory it should last a bit longer.

Its not something worth choosing a frame over, you just kinda get one or the other and cant change it

just two different head tube sizes there hass you can't use 1.125" on your pista it is a 1" head tube and steerer

Stiffer steerer, larger surface area for joints (alloy frames benefit more), makes all that area stiffer (generally. A stiff steerer tracks much better. A stiff headtube and fork also track better. They are moving to 1.5" lower bearings for stiffness now)