Blown Turbo Gasket?

I have a 89 300zx twin turbo and I have the following symptoms: Turbos dont kick in until around 4500 rpm, when it gets to around 4500 RPM white/blue smoke comes out exhaust, running at half the power it should, runs rough at low RPM, uses oil but there are no leaks, oil pressure reads good when first started and sits at halfway mark but when driving it drops down to the quarter mark. I was told this is a turbo seal that is blown, also smells like unburnt gasoline or burnt oil. Care to shed some light on the situation?