I think you should first ask the question of whether you want to trust your photos to a 5GB microdrive. Given the relative reliability of microdrives to flash and the price of 1GB compact flash nowadays I would far prefer to use two 1GB CF cards than a 5GB microdrive.

In fact, even if someone gave me a 5GB microdrive for free, I still wouldn't use it in my camera.

To answer you actual question, your couple of years old microdrive is likely to be quite a bit slower than a decent speed CF card. Even the recent microdrives are slower than CF:

http://www.robgalbraith.com/bins/multi_page.asp?cid=6007-7699

Do you actually need 5GB card ? Unless you are going to be shooting RAW+JPEG all of the time and shooting many hundreds of photos a day you won't need 5GB.