Stability will be fine - I cannot remember when mine last dropped due to anything on the line from house to cabinet.
ADSL line length means nothing ... the cabinet being four houses away, assuming you are routed directly to it and not round the estate, would suggest less than 100m and that should give 80/20 or close to.
The standard BT modems are fine - yes upgrade if you want to and your choice has functions you need but in almost every case the two BT modems do not cause any issues.
M H C
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