good way to phrase the question rinse. Let me reiterate what i have said before on this subject. you might notice that i have an 80 and a 40 as external firewire drives. I had the 80 first. I got the 40 because the 80 was just too much trouble. After it got to be a little over half full, it began to take tediously long times to do almost anything with. It takes forever to search, forever to run diagnostics and repairs, forever to defrag, forever to to do anything that requires scanning it. It also increases intial boot times as it must access larger amounts of volume info. In general it is more of a pain than a great thing. also keep in mind that you will lose a certain percentage of it to formatting and it really only turns out to be a 75. while this holds true of all drives, it becomes much more evident when 5 gb just seem to disappear.
While the amount of files, and the size of files has a lot to do with this, it is my experience that up to about 40 is reasonable. after that it starts taking more time than it is worth. My 80 has taken almost 24 hrs to run repairs on and over 13 to defrag at times. and without degragging, it is a nightmare of screeches and delays.
but if you are planning to fill a large drive with a few large files like video captures, then a larger one might be ok. Otherwise, at a certain point you are paying for more headaches than utility. In the future i do not plan to buy anything larger than a 40.
i would also add a word of warning about maxtor's customer service. it is more like dis-service. While mine works fine, it is because of the vast amount of troubleshooting i have done. Maxtor's service people have been some of the stupidest people i have ever dealt with. when i first set mine up i had difficulties. their answer was for me to return the drive to rule out a faulty unit before they would even attempt to give any further help. After having solved the isue on my own, i wrote them several times about it and never even got a reply back acknowledging my email. so if customer service is important to you, i would look around some more.