[CSX 4133]

My first hand experience of actually racing a small block is they are competitive with a big block to a point. If the course has enough slow sections and only short straightaways they can keep up, usually under braking. But at the next straightaway the big blocks regain their advantage.
I race a period correct small block making about 438 HP in B Production vintage races, whereas the A Production Corvettes are making 700+ HP, something the 60's Corvettes never achieved but that has as much to do with the manner the GCR's are written as the specific race course.
A track like Sebring, Road Atlanta and Road America cubic inches wins out due to their configuration. A track like Sears Point with it's less technical aspects a small block can keep up with a big block, all things being "equal".
The big 427 came to be as a means to try to overcome the Shelby's drag coefficient and achieve a higher top end on the courses with the long straightaways. But in doing so it presented additional issues with brakes, front end lift and cooling.
Not taking sides, both motors have their place, and I enjoy both equally.