UK model V166-K new official firmware now released v4.2.3.BT
https://www.draytek.co.uk/support/downloads/vigor-166

Has the new firmware sorted out the massive speed drops and huge upload latency spikes? I noticed the modem codes are the same which is a concern that if I put this back up nothing has really changed. I don't want to loose 10Mbps and have latency spikes of 200-300Mbps on the upload side again.

Okay you can't flash the EU using the UK version of the firmware but you can use the download from the international web site. There's been another update to the firmware which is now 4.2.3

Hi guys, just installed my Vigor 166 today. We’re upgrading to a G.fast connection on Wednesday and I want to use my current router which I recently bought.

I have to say, I’m noticing some odd behaviour with my connection so far (on a VDSL line currently). The download used to be consistently at 70mbps, not varying between 30-50.

The upload is just weird, when I do a speed test it goes up to 16mpbs, freezes, then falls to about 3mbps and then ends up climbing to 18 (which is the highest I’ve seen it).

I am really concerned about what I’m reading as there doesn’t seem to be any Gfast alternatives outside of eBay or Alibaba - I just don’t trust buying a modem from someone random online.

A stable connection is really paramount as my household have key workers that have to have stable internet. The reason why I’m upgrading is to improve it, so if the 166 isn’t going to do the job, I’d be keen to cancel the upgrade.

Any advice would be much appreciated. If I’m being totally honest, I’m freaking out a bit. Some people seem to have a great experience, others seem to be plagued with issues. All a bit worrying...

You could try a Zyxel XMG3927-B50A G.Fast router, a few ISP's have been issuing these recently.
It has bridge mode, so it can be used as a G.Fast modem if you don't want a full router.
The only problem I know of is that, in router mode, it doesn't work with BT TV subscription channels.
This is a known problem with many Zyxel routers, in the past the fix has been to allocate concurrent WAN to the port connected to the BT TV (YouView) box.
However there is no concurrent WAN option with the current XMG3927 firmware.
The retail model goes for about £150, but check out eBay for people selling off ISP issued units going cheap.

Thanks very much for the suggestion. I’ll do some research into the bridge mode and turning off the wireless as well. I know the Gfast Asus router/modem combo has issues with that so just to make sure the Zyxel is suitable.

It’s crazy that the Vigor 166 seems to be the only Gfast modem available to buy in the UK at the moment