[aerohead]

My home library paid off on some 'numbers.'
1) Speedsters have a 170-pound weight advantage, compared to coupes.
2) The mutilation of the Speedster roofline, compared to the Coupe results in a 10.4% Cd penalty.
3) The added mutilation of lowering the roof and side curtains of the Speedster results in a 18.6% Cd penalty, compared to the Coupe.
4) Top speed of the Speedster, compared to the Coupe suffers a 2.65% loss.
5) Fuel economy is 10.2% lower than the Coupe.
6) The Speedster does have an acceleration advantage up to 28-seconds elapsed time, then is overtaken by the Coupe all the way up to terminal velocity.
7) In the 1/4-mile, the Speedster is 0.6-seconds 'quicker', and 2-mph 'faster' than the Coupe.
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For the 356-to-Beetle comparison, things get interesting:
8) The Beetle has a CdA 0.891 meters-squared vs CdA 0.4635 meters-squared for the Speedster.
9) The Beetle's test weight was 2,130-pounds vs 2,110-pounds for the Speedster.
10) The Beetle' Road Load @ 60-mph = 161.6-pounds vs 102.0-pounds for the Speedster.
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In 1952, The 356-A could hit 103-mph on 65-bhp.
MGs and Austin-Healeys of the same 'size' required 100-bhp for the same speed.
* The #44, Porsche 550 Renn Sport, two-man 'COUPE', by race builder Walter Glocker was clocking 116.88-mph at the Nurburgring. This car was reported @ Cd 0.232, by Erwin Komenda, in scale wind tunnel testing, and Cd 0.36 @ full-scale, vs Cd 0.45 with the 'Spyder' ( roadster )[ Hucho ].
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To have a chance at 100-mpg, you'd want to ditch the 'full' wind screen ( Windschutz-scheibe ), the Porsche 'aero-screen', and go with Walter Korff's single-occupant 'bubble' screen, full side side windows ( seitenfenster ), full head fairing, slow diffuser, and boat tail, as Knot Farrington did with his Ford Thunderbird Bonneville streamliner 'Hel's Angel'.