All circuits go from you to the co to the customer. That total distance is the distance of the loop. Ideally you'd be a clec and colo this stuff in the co and only pay for one link, not two. Also, the costs would likely be MUCH less to a clec. Total cost is based on distance.
Distance is from pop to co to customer.
Longest I've heard of is 256ish at 29k' using Net to Net sne2000. These apply equaly for any type of service. You'll likely be doing the same thing with dedicated t-1. It's just that with DSL you are paying less for the install and less for the local loop. Same level of service out to the customer, different transport.