Only posting if will give a light to the technicians which must be aware on this thread by now

The units shipped to Greece they came with 3.7.4 firmware (3.7.3 seems shipped for UK market) ... i am not sure if they are compatible with the UK market (it should be the current firmware the guys is using it with Annex A) but here is the link if anyone want to try it ... is from Lexis.gr , official support for Draytek Greece
http://www.adslgr.com/forum/threads/793191-%CF%81%CF%85%CE%B8%CE%BC%CE%B9%CF%83%CE%B5%CE%B9%CF%82-draytek-2860n?p=5374569#post5374569
https://rapidshare.com/share/0C4B324A0F7AE4A5D937AD149A16FC3B
Once is the *all* file, a master reset should be perform right after the firmware upgrade

The 2 guys using the unit with the 3.7.4 did not had drop out as far i am aware, till they jumped to 3.7.4.1, going back to 3.7.4 the drop outs stayed even with the 3.7.4 even *rst* file was used reverting back firmwares
Not sure if draytek using different wi fi drives for each firmware .. if this is the case then a reflash of 2-3 times in a raw (same firmwares) may helps change the drivers

EDIT

Perhaps before or after of any firmware change a 30/30/30 hard reset may helps for the current situation for the unit to clear the memory
If google it should give the exact process

I have tried before the 30/30/30 hard reset with a 2760n and seems was running smoother

I have edit my previous post ... please read it again ... the guides of 30/30/30 hard reset & reflashing 2-3 times the same firmware (if is wifi driver change) apply with any other firmware and not only with the one from the link

babis3g wrote: Not sure if draytek using different wi fi drives for each firmware ..

My thoughts were that maybe the WIFI card firmware was updated along with the later firmware IIRC these units have a separate slot on the board for Wifi hardware, it is not a Solder on mobo type.

this is however purely speculation, and i would like to be proved wrong!!!

*** EDIT ***

I guess it would be nice to actually know EXACTLY what was contained in the firmware updates.

babis3g - i will try the 30/30/30 reset, and probably try applying the UK 3.7.3 again, note this is different to the UK 3.7.3.3

only the changelog below i can find
ftp://ftp.draytek.com/Vigor2860/v3.7.3.3/Vigor2860_v3.7.3.3_release_note.pdf
ftp://ftp.draytek.com/Vigor2860/v3.7.4.1/Vigor2860_v3.7.4.1%20_release_note.pdf

I also not sure of course if is different from the UK release but i am sure 100% all firmwares i have in my hands ( i also have the 3.7.1, 3.7.2 don't ask how i got them as i am a draytek fun) all are from the draytek main official site in Taiwan

The 3.7.4 is also from the main offices at Taiwan and posted in the forum by a draytek official officer & not by me ... None of me or draytek greece are touching (modifying) the firmwares ... are just how came from the main ofices

Seems to me the most comprehensive list of firmwares is on the Taiwan ftp server. I guess these would be the most up to date before they deploy them to regional areas subsidiaries.
Has the most apps like smart monitor / vpn client / firmware flashing tools...etc.

ftp://ftp.draytek.com.tw/Vigor2860/

I had a response today from draytek, they provided me with a Beta firmware image, that didn't resolve this specific issue.

I did ask if there were release notes that describe this particular issue, or whether it was the standard tech support "try this new firmware" lark. It appears to be the latter.

I've noticed that the problem seems more prudent if I transfer a lot of data through the wireless, if your not you get three standard windows pings that will jump from about 6ms to 230ms and back again. Just as a guess, could this be something to do with the WPA2 key cycling? Has anyone tried using other encryption on the wireless (obviously this restricts the 802.11n speeds)