Hi Davey,
Can't tell you about v3 but as someone who wanted a LB but first settled for a GR v2 only to ultimately go for a LB I'd say that the LB is the much superior ride! Absolutely love my Bolt - best frameset I've ever ridden (and have ridden quite a few...Reynolds 853, 753, 653, 531 amongst them.)
Don't get me wrong: the GR is a great introduction to low trail etc but it doesn't ride like the LB does. The former perhaps does a little better for light touring, probably due to those stout rear stays but the Bolt planes man! ;)
The GR is very low and low, a bit odd for a Randonneur style frameset (aesthetically at least.) Have you compared the two on here?
I consider my LB to be my (all) road bike nowadays but am looking for a used Sam Hillborne here in the EU for longer loaded trips. It'll be good to be able to eventually compare the two, with a bit of luck!
Hope that helps a bit 👍