The other difference between a big block and a small block is you cannot get 600 ci from a small block, but it is easy money with a big block.
The weight of a big block might be around 100 lbs more which is about 4% extra in a 2500 lb car. The possible extra power (all things being as comparable as possible in the engine builds) from the additional cubic inches (say 540ci vs 427ci) might be 26% (just ratioing 540/427)...
So, it is clear that the detriment of the extra 4% in weight is easily outweighed by the benefit of the extra 26% in power by going from a 427 small block to a 540 big block.
Tough to argue with those numbers!
There is (still) no replacement for displacement