I prefer the GH2.From viewing the Grado site, I believe:
SR80e same as the SR60e, except de-stressed drivers
SR125e same as SR80e, except 8-wire vs. 4-wire cable
SR225e same as SR125e except L-cushions and closer driver matching (0.05dB vs. 0.1dB)
SR325e same as SR225e, except different driver housing (Brushed Aluminum) and leather headband
I am trying to decide which Grado to buy. I have the old SR60, which I recently compared to a friend's SR80e. The SR80e is crazy efficient but I have three headphone amps, so efficiency is not a factor. No significant difference in bass or mids that I could hear, the highs on the SR80e were more detailed, but unpleasantly aggressive with some music. Based on this demo, I know I need to shop higher up the range. I had considered the SR225e and SR325e, but the GH3 and GH4 are on sale, which makes them an attractive proposition. The GH3 is priced exactly in between the SR225e an 325e.
I've had the RS2e on loan a couple of times. I like them a lot, but overall I prefer my Beyerdynamic DT 1990 Pro. According to this comparo, https://majorhifi.com/grado-gh4-vs-beyerdynamic-dt-1990-pro-review/, the GH4 and DT 1990 should be close in overall SQ. If I were shopping for the best Grado in my price range, the GH4 would seem to be the obvious choice, as they are about $150 CA less than the RS2e right now.
I'm not looking to replace the DT 1990. I am looking to improve on the SR60, so I maybe don't need the highest fidelity. The GH3 costs $200 CA less than the GH4. The GH3 has S-cushions, which I find more comfortable than L-cushions. According to Major Hi-Fi, the GH3 has less bass and resolution, but smoother highs. Lower resolution and less aggressive highs may actually be an advantage for times when I listen to Google Play or YouTube Music. Do you have any advice for me?
He has in my opinion the best conditions to become the best Grado ever, even with the best value for money.