I'm looking at getting some new wheels, but I also long term want to put around 650+hp in the Z. What's the likelyhood that much power will crack or break spokes on the wheel itself?

 

extremely unlikely. your always limited by the traction of the rubber; and to that extend; your not likely to find a rim with enough rubber to have a problem. unless your running like 2" wide drag slicks on a top fuel racer.

at some point they do have to put bead locks on the tire so it doesnt spin around the rim; but again; your up in topfuel category, a ways from 650hp, or anything else a Z will put out.

 

You'll pop your rear axles before you break a quality wheel from a dead stop with hi-torque (has happened already). Can't find the thread now, but there's a company making stronger axles for the Z now due to this happening.

 

Driveshaft Shop makes axles, Forged Internals sells these.