either casting can make nice power if your shooting for more drag oreintated you should start with a cub. if for more rideable ( depending on your description of "rideable") shoot for a PORTED serval. most as cast servals left banshee owners somethign to be desired. i felt they did what they were meant to do adn deliverd lower port timings to make a "builder" have to work for a good running motor.. cubs you can go in there and fart around with a file and build the motor half ass right, run it on alcohol, buy "drag parts" and blamo you got a decent drag mill.