correct me if I am wrong but i thought the line-height w/o units was used a coefficient. so line-height:8.0; will yield 8 times the height of the specified font-size for the element!
Aesthetically, I have to ask why so much "white space" ( roughly 3.5 times the X height bove and bellow your text???) and this is w/o taking in to consideration users with different settings or system ress. Are you actually wanting to set a fixed sized image background and are trying to convert ems to px?
The other flaw is , tho it may be inconsequential since all your links are one word but I like to plan for worst case scenarios, that if your link text wraps you will have THAT MUCH space between the two lines!
ditch the line height, no-wrap and padding might work. but the question is what are you vertically centering in relation and proportional to? because what you are saying is that you want.
line-height doesn't make big text. It sets the spaces between lines, so such extreme line height sets HIGH lines but doesnt enlarge your text.