James wrote - " I think that the automatic slippage allows the turbo to hit its sweet spot sooner." No matter what, the turbo won't help much right "off the line" but to me its (the automatic) biggest advantage is being able to keep the throttle down and the boost up when shifting. For simplicity of service I'd avoid going to a turbo (we've owned many, 240,940 and Saab models).
A bit more torque through cam, compression ratio and exhaust would probably offer the most bang for the buck.
The AW70 can be modified to get more positive shifts by eliminating the "cushion" (my term) pistons located above the valve body as they are in the AW71.
To me it makes more sense to upgrade the suspension first by going to aftermarket bars (or snagged from scrapped Turbo models) and quality performance shocks and tires. -- Dave