Crofter
Addicted to ArboristSite
I believe most full-blown race chain is filed way back, probably for both reasons.
Niko has been doing his home work! Especially on a small saw, you have to keep the kerf down and the rpm up. With the limited torque you have to use more technique than brute strength. The total weight and the weight of each chain element that is continuously being redirected around the race course does take power; I think TW calculated a figure that was a good fraction of a horsepower. Not much on a 3120 but a much higher percentage of the available power on a three horsepower saw so more concern on a bumblebee saw.
You can make a .325 chain fast but the tooth height makes it difficult but not impossible to get the angles you need when handfiling. You tend to wind up with too tender a top plate to keep from cutting too badly into the tie straps. If you are grinding you have a few more options in the angles you can dress the wheel to.
Unless you take the cutter back a fair bit you will have effectively too low a raker anyways for a fast chain on a small saw especially with a full size 3/8 chain.
Below is a picture of the kerf of a new 3/8 chain and beside it the kerf after it was highly modified to narrow the cut. That was an experiment but I actually took the concept too far and it some things (like a knot or hitting the wood a bit crooked) would cause a jam but it sure would cut in a fraction of the time. Something a little less extreme would be better, but it gives an idea of the concept. Here it was cutting a full 25% less wood plus weight saving on the chain.