Well, I would suggest you use whatever the card originally was. The problem is, I have no idea what the default was. Here's the thing with cluster size (which is more specific to fat32; ext filesystems use block size) - the larger the cluster size, the faster the card will be, but the more space you'll waste. The smaller the cluster size, the slower the card will be, but less space you'll waste. It's a trade off, really.
Files are basically broken up and stored in clusters. If a file is 64 KB, for example, it will take up two clusters if you set it to 32 KB. If you set it to 8 KB clusters, it will take up 8 clusters. What that means is, it takes longer to get the file when it is split up among more clusters. The thing is, you kind of want that because if you set your cluster size at 32 KB, 32 KB is *technically* the smallest file you'll ever have. What that means is, if you then have a file that is 1 KB, it's going to take up the entire 32 KB cluster. So, if you have 10 1KB files, they would take up 320 KB, rather than 80 KB if you'd set the cluster size at 8 KB. The general rule is - if you intend to have a lot of large files, a large cluster size is a good idea. If you intend to have a lot of smaller files, a smaller cluster size is better. That being said, I'm not looking at a few tables of cluster sizes compared to partition sizes, and 8 KB looks like a good number to set it to. Like I said, I just don't know what the card was originally set to. If it seems slow, reformat it with a higher cluster size. It should be fine, though. Like I said yesterday, 32 KB seems kind of high.