'I would be' is like a potential hypothetical, i.e. if something would happen/be the case, then I would be happy in the present and to some degree, in the future. Example: "I would be happy if I won the lottery." It's sort of like the Imperfective, НСВ, where my happiness would be a process. Generally, this has to do with hypothetical present or future conditionals. 'I would have been happy' is more analogous to a hypothetical past perfective, СВ. Example: 'I would have been happy if I had won the lottery.' My happiness and the winning of the lottery would have been a 'completed action' like the past perfective in Russian. Generally this is used to express past conditionals. From your example, you could say it both ways, with slightly different meanings: 'I would be a good model if I was a woman.' You would be 'in the process' of being a good model, if you were a woman. Like the Imperfective. 'I would have been a good model if I was a woman.' It implies that--in the past, a completed action, analogous to the past perfective in Russian--if you were a woman, then you would have been a good model. In this hypothetical, maybe you're a 80 year old, who hypothetically, if a woman and in her younger years, would have been a good model.

Firstly, I would like to correct this statement which should read: "It could have never happened". And also "I would have been a good doctor had I studied medicine." But in conclusion I completely agree with you these statements are true

Some replies here suggest that 'would have been' can only be used to refer to an event in the past. This distinction came up recently in another question in which a football player was injured and unable to play. It would be possible to say that 'he would have been in the team [if he was able to play] even if the game is still in the future. At the time of the statement he cannot be in the team, but the speaker is making the statement from the perspective of the future. Looking back from the time when the game will be played, he would have been playing if he was not injured.

Just think of "would be" (indefinite/not definite, present or future) and "would have been" (indefinite, past) as something possible but only under certain conditions.

correction: "were", not "was" Whether or not the situation would be possible has nothing to do with it. The thing that matters is that the situation is imagined, hoped for, or, yes, impossible. However, it can be possible. For example: "I would have a big house if I were a rich man" in which being a rich man is not impossible. Your two examples are not different. Claire is correct. The only difference is time. All of these are acceptable: I would be a good model if I were a woman I would have been a good model if I were a woman I would be a good doctor if I had studied medicine I would have been a good doctor if I had studied medicine