I bought a 10" metal cutting wheel for a miter saw to cut aluminum, but
it really doesn't work too well. It cuts it, but it's not a straight
cut, presumably because the cutting wheel is flexible, and the motor
isn't fast enough.

I ordered this blade "http://www.amazon.com/gp/product/B00006407O" but I
may return it unopened if it's not going to work well.

Is a 14" chop saw necessary for cutting aluminum (3/16" flat bar)?

Are most of the chop saws 14" because this effectively lowers the speed
of wheel across the metal?

I saw a 6" chop saw that runs at 9000 rpm, which is close to the speed
of a 14" chop saw running at 3900 rpm.