In my experience, there are two things that impact your eMule performance.
1. The ports. You can use the official eMule port tester, but make sure that you're really forwarding the right TCP ... AND ... UDP ports in your router or
firewall.
2. You have to let it run. You will NOT get good speed right away. Leave it running overnight and I think you'll find your speed gets better.
However, sometimes you just can't catch a break with eMule. I've had times when - as you mention - I have hundreds of people who have a file, and yet it's only coming in at 5K/sec. but then other times with only a handful of people connected, the file shows up at lightspeed.