If you are going to use a external gate, you can use a internally gated turbo. Just remove the actuator and tack weld the waste gate valve closed on the outside of the turbo where the actuator rod would normally go on. A BOV releases pressure between the throttle body and compressor wheel when the throttle is closed which puts less stress on the turbo. The waste gate opens when the required boost pressure is meet so it won't over boost. This is done by controlling the amount of exhaust gas which goes through the turbine. So to answer the question, you need both a BOV and a waste gate