What CPU are you running it on and how many cores are being used? Are you also in really large rooms like Techlore and Matrix HQ? Because I think I'm in all of the largest rooms (and a lot of the smaller ones)
If you want to go cheaper and have only 300-400 Mbps of bandwidth, I've heard lots of good things about this provider:
Note that many significant improvements have landed very recently, for instance the chain cover stuff which significantly improves handling of rooms with frequent membership changes (such as the aforementioned bridged IRC rooms).