Would it not be the lesser of what ever the best speed your line can provide or your profile setting. I don't think the modem would go over the profile settings even if the line could support it.
If for some reason your line slowed down to external issues (moisture damage / tree rats / etc.) your modem I thought dropped down to the best speed it could provide no matter what your profile is set at. And then it locked in at that even it the line was fixed. At that point you would need a reset.
The profile I thought was the theoretical maximum that the provider (MTS) thought that the customer should be getting based on wire gauge size and line distance from the Dslam.
But I could be wrong on all of the above!