Mixed for me is probably the hardest of all to play competitively. It's really fun to play mixed socially, especially if your team is mixed and the other team isnt, haha.
As a 4.0 woman playing 7.0 you will have to be really strong at net and you will probably not be allowed to many (if at all) errors. The dynamics here are so great since the ability range of a 3.0 is much wider than a 4.0.
As a 4.0 woman playing 8.0 you will have to be able to keep the ball low at all times on volley exchanges, put away balls close to the net with overheads, or at least push/cut the ball deep or at angles that will close the point at least half the time.
As a 4.0 woman playing 9.0 you're probably not a 4.0 and you probably know what you're doing.
As the woman they will probably pick on you, but I think you like that. I can actually see you doing better in time at mixed (with a good partner) than in womens.
"In the 1980's two men dominated--sometimes each other, most of the time everyone else."