It is my understanding (I have very limited understanding
) that the chip controls the WG solenoid. As it pulses the WG (On/Off) more often, the Duty cycle increases, and the boost rises. In essence, it "bleeds off" more boost so the WG actuator does not open as quickly.
Now, the stock 87 boost level was around 16 psi and the HA was set at 12 psi. It is my belief, this was accomplised as follows:
1. Increased WG DC
2. "Y" orifice size (Not documented as of yet)
3. Actuator
The stock turbo on the 87 also pushes around 400 CFM v.s. the 300 CFM on the stock HA turbo. With the more efficient 87 housing in addition to the intercooler, the increased density of the air charge requires more fuel (Read higher injector DC)
The 87 ECM upgrade is a GEAT one, but will cost around $210 with a TT chip.
Back to your question:
As Brad stated ......... Your car will run with the stock 87 EPROM ......... how well it will run is a matter of testing, observing the vital signs (recording capable scantool) and how picky you are with the tune.
In the end, it all comes down to your goal and budget. Speed = $