We changed to Shaw 25 about 8 months ago and have seen a noticeable decrease in speed ever since. Though we should have had about, "up to 25" we never achieved over 15. Recent speed tests via Shaw's speed test site show we have dropped down to 7.5 average - we are now fully in the category below the one we are paying for.
I will likely be contacting Shaw about this issue very soon as we are about to actually need the bandwidth as our business starts ramping up online activity.
Our situation may differ from yours, as you do seem to get your speed-test near where you expect. However, the issues may still have relationships behind the scenes.