When you signed up the Zen site you may have seen an estimate
"144.0 - 160.0 Mbps
TYPICAL DOWNLOAD RANGE"
which is what they show for unlimited fibre 3, but this appears to be the same estimate for a wide range of distances from the pod, once it reaches the point where most would say G.fast won't work it changes to
78.0 - 160.0
TYPICAL DOWNLOAD RANGE
So the real question is once entering full address and phone number what did they suggest your speed would be?
Zen Internet is signed up to the Ofcom Speeds code of practice so if the speeds do not reach the minimum speed given during the sales process you can walk away or accept a downgrade to a different product with the pricing changing to reflect that.
260m to the pod, is edging towards the limits of G.fast and as wiring does not always follow a straight line then might be longer.
I know the limit is around the 300m mark, so I was a bit skeptical at first at the speeds but:
The speeds I've been quoting is after putting in my address and phone number: both in the dsl line checker and on various ISP sites.
Sky - 148-149. Min 100
BT - 137-138. Min 100
EE - 145-146 Min 144.
Zen - 144-160 with a typical speed of 160 (I think that's their guarantee, but they don't explicitly state this).
All had upload speeds around the 20-25 mark.
The limit on speeds is more on the 300/50 product where my speed is limited to 184.6-289.4. My upload speed is capped at 22.9 as this is the expected speed even at the 300/50 product.
For comparison, if I were to live much closer to the cabinet (w/o phone number), my advertised estimated speed would be 297-330, typical of 330 and upload of 44.2. This is why I was comforted in thinking that the speeds advertised were what I would expect since it looked like the distance was already factored into the expected line speed. It appears that the speed restriction occurs on the 300/50 product as my line can't meet that due to the distance from the cabinet. But the 160/30 is able to be met.
Zen seem to think that something is dampening the line speed. If that isn't the case and my speed is hard capped at 100, then I'll have to downgrade. the 30% odd increase in speed isn't worth the premium. Plus the £55 wasted on the engineer installation.