just a note .... that upload cap should be in the neighborhood of 80% of your upload speed. Your download speed may be substantially higher than your upload, depending on your service provider. Virtually all DSL and Cable providers do that, and the data rates are typically in the neighborhood of 10:1 or worse download:upload (so like my connection is 7mbit down, 256kbit up, worse than 25:1).

I'd recommend turning the upload way up, really really high (like, 5000KB/sec on a very busy torrent (anything new with more than a couple hundred peers). Then see how fast you actually upload after a couple minutes (your upload will end up choking your download, more likely than not), and seeing how fast it actually gets uploading.

While you're doing that, you might watch your network latency by periodically pinging a well-known good-pinging site, (google, your isp's webpage). If your ping time is in the <100msec range, you're doing good, if it's more than 100 msec, you're starting to choke, and if it's mroe than 500, you're probably as saturated as you're going to be able to push your link.

Then set your max upload to 80% or so of that peak speed, or that value minus 15-20KB/s, whichever feels more comfortable (ie: if your peak is 150KB/sec up, cap it at 120 or so, if your peak is 80KB/sec up, cap it at 60 or so, if your peak is 35 up, cap it at 20 or so).