The "best turbo motors" that are optimized NA first have well-designed and laid out turbos, which have ~equivalent backpressure as boost. So, an NA cam works the same for the turbo since the intake and exhaust pressures have been raised equivalent amounts. However, a turbo kit such as STS has a bit more backpressure than boost, so things change a bit.

The overlap on a turbo is bad NOT because boost is lost into the exhaust. Quite the opposite, though. The 20 psi exhaust will overcome the 10 psi intake during overlap and dilute the intake charge.

Mike