number of files in a dir vs. performace

I'm using mysql to hold references to image files then served on my pages via PHP. I have typically a set of two files: thumb and a large original, on occasion there is also a variant inreasing the set to 3 per image currently I am holding all of the files in 1 directory since the DB can keep track of them, however their number has grown to over 400 at this point my issue is whether it would be worth it (performance wise) to split them into thumbs and works thus having 200+ files per directory as opposed to so many, I am expecting the number of images to double in the future. R> ________________________--__-______-______________ eat pasta type fasta