It's a good question. I'm not very far into the process.. a Sturmey-Archer 8speed runs about $170, but I see they have a 28 spoke for 155mm axle, and a 36 spoke for 170mm, and I'm still not sure if the 28-spoke hub is the right size (anyone know the axle length on the Curve?) The LBS tech said he may be able to re-use the existing rear wheel spokes since the bike is new.

It's not a cheap upgrade, for sure. Oh, and Sturmey Archer said if I could wait a couple of months, they have a new 8speed internal hub coming out with a wider gear range than the current model. But, two months is like a lifetime....