of course there is a case where a specific modem code as example may work in general (or for most users) better with a dslam vendor ... but really i think the answer is below, so it may depending each line user
http://www.draytek.com/index.php?option=com_k2&view=item&id=1226&Itemid=293&lang=en

Just to be clear, vectoring is a VDSL technology, has no effect on ADSL. Vectoring is not supported by any UK ISPs currently. Vectoring is not part of the official product specification yet.

For what it's worth, I'm on BT Infinity VDSL. These are the effects of loading various 3.7.8 firmwares:

STD - CPU usage went down slightly, otherwise no changes.
VECTOR1 - Web interface took much longer to load pages, severe decrease in sync speed & internet speed.
VECTOR2 - Web interface took slightly longer to load pages, otherwise no changes.

Whatever the cause, unless you on a Vectoring trial, it's not vectoring
making the difference there...

Admin vectoring aside please could you tell the difference in the two modem codes on the STD firmware? By default the lower version number is used, but I changed to the later version number with no problems...

I recently switched to FTTC 80/20 from Xilo https://www.xilo.net/adsl_broadband/#pro , which is essentially a re-sold BT connection.

I found it looses connection frequently with 3.7.8 VECTOR1 and 3.7.8 VECTOR2, EVEN WHEN g.vector IS TURNED OFF.
The connection is stable with 3.7.8 STD, but it comes at a speed penality and also seems to switch to interleaved.
3.7.8 STD only syncs at 75Mbit/s down, whereas both VECTOR versions synced at 79Mbit/s down (attainable speeds are also lower on STD).
This is on Infineon equipment (IFTN).

Stats and options copied below.
Incidentally, I noticed that 'retx' shows as 'ON' for downstream, I understand this is what BT calls 'G.INP', can anybody confirm that?

> vdsl status

---

ATU-R Info (hw: annex A, f/w: annex A/B/C)

---

Running Mode : 17A State : SHOWTIME
DS Actual Rate : 75324000 bps US Actual Rate : 20000000 bps
DS Attainable Rate : 93112496 bps US Attainable Rate : 24547345 bps
DS Path Mode : Interleave US Path Mode : Interleave
DS Interleave Depth : 0 US Interleave Depth : 0
NE Current Attenuation : 13 dB Cur SNR Margin : 6 dB
DS actual PSD : 0.-3 dB US actual PSD : 14. 0 dB
NE CRC Count : 0 FE CRC Count : 0
NE ES Count : 0 FE ES Count : 0
Xdsl Reset Times : 0 Xdsl Link Times : 2
ITU Version[0] : b5004946 ITU Version[1] : 544e0000
VDSL Firmware Version : 05-06-00-08-01-06
Power Management Mode : DSL_G997_PMS_L0
Test Mode : DISABLE

---

ATU-C Info

---

Far Current Attenuation : 0 dB Far SNR Margin : 6 dB
CO ITU Version[0] : b5004946 CO ITU Version[1] : 544eb204
DSLAM CHIPSET VENDOR : < IFTN >
> vdsl optn status
trellis [US] = ON, [DS] = ON.
bitswap [US] = 1, [DS] = 1.
[0: default(ON), 1: ON, 2: OFF]
sra [US] = 4, [DS] = 4.
[0: default, 1: MANUAL, 2: AT_INIT, 3: DYNAMIC , 4: DYNAMIC_SOS]
retx [US] = ---, [DS] = ON.
aelem ON
G.Vector OFF
>