if its direct line routing and decent cabling you should be a comfy 80/20.
Possible caveats I guess are.
Been unlucky on the crosstalk lottery, but you should hopefully not have to worry about this in early days of service. Bear in mind I only held onto my 80+ attainable for 3 weeks
and I was first on cabinet but I am probably one of the most unluckiest people in that regard. Even if this is the case tho it should still blow anything adsl can do out the water.
Having bad cabling like ali or thin copper may reduce speeds over the distance.
Possibility of indirect line routing.
Also distance from exchange to cabinet is a factor, it affects adsl power cutback, on my line its pretty brutal whilst kitz has hardly any as she is close to exchange, I estimated on my line its around 10-18mbit of lost sync speed for adsl power cutback. apparently tho its sort of mid to longish e-sides that suffer the most, if the e-side is really long the power cut back eases of again.
You should be good for an easy 80/20 tho.
Your estimate makes me guess approx 300-400m for actual line length.
Openreach support (yes they do exist although normally only for isp's) told me my line was just over 400m (I think cant find the email now), but today I was told its about 220m.
Possibly.. My estimate from the BTw checker before I got FTTC said 'Up to 62.6' Mbps
haha :0 yeah mine was 73 plusnet sign stage and 65.9 when I signed to BT infinity. These estimates I think try to take into account heavy crosstalk. Then later when an areas has enough customers I think they then feed live data into the system so the estimates change.