I'd re-check that CO spec for your car. The spec on an '86 is 0.6, plus or minus 0.2, not plus or minus 2.0.
Like I said, mine is happy at 3.0. Having said that, these cars differ a little from one to the next, and some are modified. I have another 930 that is happiest at a diffferent CO. I'd suggest you find a good shop to adjust yours and let them play with it a little. You want the leanest mixture that is still acceptable at full throttle under load and doesn't give you driveability problems at lower speeds and loads.
Or, you could talk to someone at a shop that specializes in the 930, like Imagine Auto.