If it's not for a GFY top banner sponsor,
the button has to be 120x60
their rules not mine
I don't think it's that big of a deal personally. GFY has so much webmaster traffic even if you have a text link people are bound to click it some of the time and see whatever program it is you own or are you an affiliate of.
I don't think you are losing anything by not having a big banner.
Most of the time I click text links in sigs more than I do banners unless the banner has something really eye-catching, regardless of size
