[ZOERA-SC7XX]

The Grand Sport had bad aerodynamics, at least initially, and experienced front end lift at speed. The Cobra Daytonas were superior on long, fast tracks, but the Cobra FIA roadsters had it all on the smaller tracks. After Penske and Hall (and later George Wintersteen) got the Grand Sport's fitted with the 427's and tweaked the aero package, they were rocket fast, but were never homologated for FIA GT competition and had to race against prototypes. The Ferrari 250LM was a race-built mid-engine prototype, and probably superior on the long race tracks like LeMans. The 250 GTO's were closer competition to the Cobras and Corvettes, and were quite successful in GT.
Overall (in my opinion), the 250 LM may have been the best of these, being a direct decendent of the successful Ferrari 330P. The Corvette Grand Sport may have been my favorite, and spanked the Cobras a few times, but never got the success they would have had if GM didn't abandon racing. The Cobra Daytona was the most successful, winning the world championship for GT cars in 1965 (backed up by the roadsters).
Introducing the 427's to the Daytonas never happened, as the Super Coupe (Type 65) wasn't actually completed until 1981 and never raced, so that theory is speculative at best. A study of race results will clarify any omissions and scrambled dates. All were great race cars.