Sphinx I've only just got it out of the box and I'm still playing with the wrapping.
Phex is a Gnutella client with the ability to connect to or set up private Networks you can set up yourself.
I really can't compare the speed as yet, but one thing I have noticed is that I always seem to connect as a leaf (unlike with LW where I am usually an ultrapeer and get connected to 10 ultreapeers by default. I think I can alter this in preferences, but I'm not touching that yet. And I feel some idiot could really mess the settings up if they don't understand them.... like me.
It gives a lot more connections to hosts outside limewire ... like Shareaza, but I haven't noticed any improvement in attempts to get files off them