As I don’t think anyone could read your posts at 4 pt. size, I would guess your concern isn’t what you think it is.
You are posting at 10+ pt. to me.
Is anyone seeing lbryce’s posts at 4 pt. font sizes?
The question I would need to know to help is .. does everyone else's posts seem the right size on your screen, but your posts appear smaller ? (if true, then you are either on acid or your computer is really messed up) If you are using HTML in your post and specify 'font size=xx' maybe you aren't putting the value for 'xx' in properly. Hope some of this helps.