Lower output impedance will translate into a cleaner LOD signal. The IP4 noticeably beat the 3GS and I don't see the 4GS doing any better. User impressions are tricky, you have to counter in IEMs/headphones used, amps used, possible placebos and preference variables/conditions. I think that IP4>>4GS>3GS no matter the user because the 4 will be a direct upgrade from the 4GS because they share the same signature but the 4 has a more linear response.
Edited by Inks - 10/17/11 at 10:23am