After nearly 400 highway miles to Louisiana and back--the first such drive I've done with this car--I'm utterly pleased with the X-11's performance.
She pulled consistently all the way up to 65 mph and delivered 29 miles per gallon, which is impressive for a 30-year-old carbureted car. Having the High Output engine probably helped--bigger valves, higher lift on the cam, better breathing.
The only hiccup was a rattling noise from the transaxle while shifting into 1st and 2nd from a stop after an hour or so of highway driving. After an hour or more of rest, there's no noise, which works for me since I'm not up for a clutch job these days.
Considering the shape the car was in when I took delivery (movie coming soon), her performance is impressive.