In my experience, the 325is are the brightest Grados, closely followed by the GS1000is.
Some might like the energetic treble but I couldn't listen to them for more than 10-15 minutes.
The PS500s are very similar to the HF-2s. Warmer than the models in the Prestige series and with better bass than the RS1/RS1i.
The PS500s are also very similar to the vintage PS1s.
The PS1000s are unique.
Very detailed with nicely extended treble but without any shrillness of brightness. Bass is tight, textured and goes very deep.
The headstage/soundstage has great depth and left/right width also goes beyond the shoulders.
The PS1000s are my favourite headphones. Period.