Thanks for that, according to that, the ideal area is just in between 48-19 and 48-20, with 48-20 on the left, and it's a bit closer than 48-19 on the right. Then again, the range is so small on that graph, and it's hard to tell exactly what the length is down to 0.01" when I have my cranks and rear wheel in. This is all without half-links.

I guess I'll just have to go down to the lbs and give it a shot!