OP => you need to be careful here - because you are essentially asking two very different questions, and they have different answers.
Q1 - I need a DAP to power my IE80's (mostly), and my HD650s (the rest of the time) - what is best?
A - your clip zip won't power the HD650's properly, so if that is a criteria, you need to look at a different DAP, or add an amp. As far as what is best goes - that would depend on what feature set you wanted from your DAP.
However - if your question is more:
Q2 - I want best bang for my buck, what should I upgrade? Then it becomes a totally different question. And then I agree with SilverEars - headphones make the most difference. After that look at feature-set in a DAP, as different people will have different needs.
What are you actually asking?
If we go back to your original post - then the X5 is a very good DAP at sub $400 (look for deals) that will power both your IE80 and HD650. There are others you could consider like the iBasso DX90. Don't look for huge improvements with your IE80's though. The big gains overall will be things like ability to drive full sized headphones, ability to run as a DAC, ability to decode DSD to PCM etc.