yeah thats usually the other people's fault (the people youre getting stuff off of, servers), I usually dont get more than like 30k/sec max on stuff, and im on cable too.
There are only 2 causes for it not connecting at all, 1) The server/user isn't set up right and it's their fault (most common), or 2) irc isnt recognizing your IP fully, to fix this, do this every time you connect:
type /Dns [yourname]
Copy ctrl-c those numbers it gives you, like 11.66.44.11 etc... those ones
Go to Options -> Connect -> Local Info
Paste those numbers into both those boxes you see there, then press OK.
Sometimes that fixes the shit, other than that, I'm not sure what it would be, but good luck.