Prima Luna EVO 100/200 vs 300/400 Pre-Amplifiers

Hello,

I currently own an EVO 100 preamp that I'm happy with.  I've been debating on upgrading to an EVO 300/400 and wondering for those that have compared the 100/200 and the 300/400 preamps -how big of a difference in sound quality is there?  

 I run into a solid state amplifier and thinking the higher impedence may be a benefit - as well as the other upgrades.  But looking for experience..