My wife and I think the label 'BULL' is thrown around way too much. We get so many gents telling us they are a bull, but most of them are just well endowed. For us it takes a lot more than a big cock for us to consider them a bull. The ones that interest us are the ones that are well endowed (obviously) but have confidence, swagger, an X factor, charisma, natural dominance, alpha qualities and know how to fuck her hard and rough, but with respect and understand her boundaries. He also needs to understand the cuckold dynamic.
I am a very submissive, bi cuck, so the ones we tend to seek out, know how to work with a cuckold husband like myself and understand what my wife and I need to take away from the experience. The true alpha bulls we've met know this dynamic instinctively and have a natural inclination for it. The well hung studs, that aren't true bulls, we have found to almost be clueless of what want from the experience.