There are a few people floating around somewhere that have had G.fast installed. Hopefully they can drop by and give their experiences. I don't yet have G.fast, but I would imagine the improvements in the resync time should make those loss of syncs a little more bearable. And, to my knowledge, Seamless Rate Adaption (SRA) is enabled which will allow for the sync speed to adjust based on conditions without a resync.
I've seen your estimates and they look pretty good, so you must be no more than about 250m away from your cabinet. What estimates have BT themselves provided you with? Should be close to what the BTW checker says anyway.
I agree with what j0hn says. I'd like to add that there aren't many options for G.fast modems/modem-router combos at the moment.
There's also the ZyXEL XMG5101-S10A (modem) that supports G.fast, but I have not seen any trace of it in the UK yet and it is not MCT approved. It's another modem that won't have access to stats though (I think), which seems to be way that we're headed until some other vendors start bringing out combined units (the modems so far only really have one port for Ethernet, which may not have stats access). I have heard that Billion are looking into options, but no timescales on that.