As others have pointed out, if you are a relatively early adopter then you will, over time, see a drop-off in the noise margin. That's due to increased cross-talk. In your case, it's nothing to worry about as, at 175m from the cabinet, you'll almost certainly be able to achieve up to 80Mbps, even if all the lines are enabled. To give you an idea, the normal target minimum noise margin is 6db, and you are a long way above that. Indeed there may even be more so spare as the line card power output might be scaled back on shorter lines. If that can be boosted, there may be more potential.
For those, like me, who are further from the cabinet (700m line length), this also happens, but when it does it has a real affect in that it reduces the line sync speed (I went from 57mbps to 50mbps at 6db noise margin).
In the medium/long term, this situation may improve as there are trials going on with something called "vectoring". This involves a sort of co-ordination across multiple lines with the aim of cancelling out much of the cross-talk. If this works (and can be retrofitted), then it will improve things.
nb. ADSL was subject to the same effect and, eventually, the situation stabilises once a large proportion of lines are enabled.