I just had about 1/2 hour, before turning in, for the night, so...
The most obvious difference, is that the GH-1/G sounds more focused, than that of the Bushmills/G. The GH-1/G's bass is not deeper, but it's definately tighter. The voices are crystal clear. The treble has a bit more extension, and it' s more precise. The GH-1/G also sounds louder, at the same volume setting.
As far as price vs performance goes, both headphones punch way above their weight class. In my opinion, with the G-cush installed, the $395 Bushmills, sound like headphones costing between $700-$800.
When equipped with the G-cush, I think that the $695 GH-1, sound like $1500-$1700, so it's no surprise that they can hang with the PS1K.