the adjustment range is rarely maxed out--just because there is "enough room to do about 10 more turns" doesn't mean you should.
if you want a test of the mechanical wastegate and spring, completely disconnect the wastegate actuator pressure hose. carefully monitor your boost gauge to see if higher throttle angles and engine load causes a big spike in boost pressure. the turbo will NOT be limited in any way, so this is NOT a way to drive around--it is ONLY for a momentary test. do NOT do extended pulls like this or very bad things will happen.
if your car suddenly builds massive boost this way, then you know it is a control system issue: the ecu map, the wiring, etc. if the car is unable to build boost, then it is a mechanical system issue: it could be a massive exhaust leak, a massive induction leak, a worn out/busted turbo, a wastegate that does not completely seal/seat, a clogged cat, etc.