The most important thing about the settings, is to not saturate your internet connection. If you make sure that you assign not more than 80% of your upload bandwidth to amule, and keep the max number of connections in the 100-130 or so range, you should be fine
The number of files are you downloading and how popular those are has a tremendous effect on your download rates. If you only download, say, 5 files and there are on average only 5 sources per file, you usually will not get an average download rate of much more than 5k/s. In contrast, if you download 20 popular files (with more than 100 sources each), you should be able to get download rates in the range of 40-100k/s after a few hours.
Finally, the last two (if i remember correctly) Mac versions of aMule have a bug that limits the download speed per source to 3k/s. You can find more details
here. Right now, you have two options, you can either wait a bit until we release 2.1.4 which won't be affected by that bug (rumor is that that version should come out within the next few weeks) or you can grab my most recent CVS version (see my signature), in which that bug is also fixed. The CVS version needs to be started through the Terminal, which some perceive as an inconvenience, but on the bright side, it contains a few features (e.g., support for files > 4gb, etc.) that won't be available in the stable releases until 2.2.0.