Slow loading channel list on secondary is a known frustration, there are many more channels than the creators of the program envisaged, this is addressed by the addition of an advanced settings sheet & a fast listing option in the next patch version, now in beta testing (see
here for more details)
As to other things being slow, some figures would be useful, as one person's idea of glacial slowness is often another's idea of good speed, without some idea both of your connection's capabilities & the performance you're seeing I can't really comment, however, it IS worth noting that download speeds with winmx will
not be blisteringly fast, as you're restricted by the speed the other guy's connection can
send data, which is typically a fraction of the speed it will accept it. Also you may see better performance connecting as a secondary than as a primary as primary uses a portion of your available bandwidth purely for maintaining the connection.
We do have a test
here which is designed to give you an idea of optimum throttle settings for winmx, it should be run with winmx off.