I don't think you'll know until connected, depends on quality of line as well as length.
Also, the actual line length can sometimes be significantly more than you'd expect from the above-ground geography (though the variance is not as high as the for the cab->exchange difference, it can sometimes be significant).
It is crazy how people (not just you) but on a lot of sites are so concerned with every little ounce of speed. Anything over 20mb would be lovely,
It isn't just the downstream speed for some users: I was pretty happy with 11-ana-bit downstream from Be before I moved to FTTC, but I found the upstream speed limiting. Admittedly most home users don't work from home or want to run their own web services or similar from home, but even if you ignore P2P there are many things they do do that where upstream capability is significant. Uploading family photos and videos would be the key example and the bump from 0.4Mbit (as seen on most home accounts, of course some had the higher ~0.8mbit or more if on ADSL2+) to up-to-10mbit makes quite a difference for that even for occasional use. Off-site backups (or off-site storage more generally) is the other big one here.
Of course now I've got used to getting 75+ reliably downstream, you'll not find me volunteering to move back to 11ish any time soon! (even though for the vast majority of what I do 11 down is more then sufficient and anything more is simply a luxury).
Current Line: Andrews & Arnold (AAISP) via 80/20 FTTC, getting close to the full rate both ways, joined July 2011, upgraded from 40/10 to 80/20 May 2012.
Previous setup: Be Pro with UploadPlus (ADSL2+, AnnexM), 12ish Mbit down, 1.6 up, happy customer for ~2.5 years.