Hi Geary,
I see no one has taken a stab at replying yet, so I’ll offer my experience, although somewhat dated.
I acquired an original used GG with R2R about 4.5 years ago. I had heard a Pacific at Axpona that year and wanted to jump onto the Lampizator path. That’s where I could afford to do it. Coming from a Bricasti M1 SE, I was initially a little underwhelmed to be honest. The tone and meat on bones were there, but the resolution was clearly behind the Bricasti. Also the frequency response was somewhat uneven. So when the GG2 upgrade became available I jumped at it. I believe the engine 53 DS was the offering in the new GG2. Upon return from upgrade to GG2 I realized it still had the R2R board. I wanted the newest engine 53. So Lampi agreed to change this out.
In a short span I was able to hear the GG w/R2R, then the GG2 with R2R, followed by the GG2 with engine 53. All the same chassis, so there was a little time in between each.
Clearly the GG to GG2 was the largest leap. Very significant. Better resolution. Much more linear. Better in every way. With the change to engine 53, the resolution was better and also smoother. The GG2 R2R was very good, but with the engine 53, it was the best version.
I could have stopped here at GG2 53 and been happy forever. But of course I didn’t because of the disease. I have since moved on to the Pacific and finally (?) the Horizon - both Delta sigma. Both much better than the GG2 R2R. The Horizon is the most significant/important piece of gear I’ve owned. More important than the Taiko Extreme as well.
That being said, if I had a GG2 R2R, I wouldn’t recommend the spend to convert to the 53. Not worth the price of shipping etc. Save for a used Pacific instead.