These Origin8 Cranks come in 145, 155, and 165, and are reasonably cheap.
Amazon.com : Origin8 Triple Alloy Crankarms, Silver : Sports & Outdoors

It appears to be 130 bcd, so not super small chainrings (other than the triple)

Oh, and some Origin8 160x110 cranks (also see other links on the Niagara site).
Bulletproof BMX Crankarm Set 160mm 110 BCD Forged Black

I believe torque and stroke circumference is a linear function with the length of crank. So, shortening the crank will naturally decrease torque and increase cadence. Lengthening the crank will increase torque and decrease cadence. And, as others have mentioned, you can't just look at cadence.

I'm reasonably flexible, so I tend to like the longer cranks, but am not sure how much I can tell the difference between 170, 172.5, 175, or 180mm cranks, other than saddle height.