One JZ negative is that the only manual transmission that survives is the Supra TT 6-speed, which is about $4,500 used (+ bellhousing, clutch dribeshaft, controls). The only automatic is the TT-only A340E safe to perhaps 500, after that $$$. Serious cars use TH400.
It's very difficult to estimate the power, because different engines will not produce the same power per inch with the same boost. The JZ has made over 1,000 many times using the original block and head - there are no secrets at that level, just follow the instructions.
Personally, I would never use a BMW engine, there are too few known success stories (and those are $30,000). There is no DIY or cheap BMW speed equipment. Figure it for for a SBC, and add a zero. Don't invent the wheel, just get a wheel.
For your specs 500 is a safe bet but needs really sharp tuning for the best balance between boost, static CR, cam, intake air temperature, spark advance and A:F. 9.4:1 and 18 psi is dangerous, would have to run rich & retarded. A weak boosted engine will need to run 15 degrees of spark and 10:1 A:F at high pressure with disappointing results.
