Well, I think that if you:
Have the room for another baby,
Can afford it
Can safely have another in the car
want another baby
YOU SHOULD GO FOR IT!!!
you may well have a baby girl, you may not. However, you will love him/her and you have all the means with which to look after and bring him or her happily into the world. Seriously, one more will not make a huge difference to your family, it is already a lovely big one, so another will just fit in amongst all the rest of your lives.
I'm fairly sure that many, if not most, parents would have many children, if they could afford it, house the baby comfortably etc etc... you are incredibly fortunate and I personally think you must just go for it. you might, just might get what you wish for.
Or, failing that, you can have my tantrumming horrible, hair pulling, pinching baby girl, if you like??? >
I'd love a large family. I'd have another 3 or 4 if I were able to. I think we can manage another one. I'd LOVE a boy.
ok, so maybe not much help, but, I say: GO FOR IT. sounds like you would just like another one, deep down, you hope to have a girl, who wouldnt' after all those lovely boys? However, if you have a boy, I dont think hand on heart it will make a difference