Oakape, in days gone past the domestics flew agreed speeds - 737 at 300kts & A320 at 320kts for instance. Now they just fly the econo descent as well, although generally it's at the upper end (at least it is when I ask). Tiger is the exception as they seem to use 320kts.
We expect International heavies to be slow so plan for it - I generally allow you guys at least an extra minute or two over a domestic when on descent as you tend to descend earlier & are slower inside 30 miles. Occasionally we get surprised and someone is doing 320kts.
Your actual speed only really matters when you're in trail with another aircraft & then we'll ask or give you a speed if needed. We'll increase you if it looks like you'll be later than expected at the fix, although that only works so much (too late & we drop you a spot in the sequence instead) - being late and a heavy is a bad combination on final for the following traffic.
In summary we expect profile, whatever that is on the day. So keep doing what you're doing & we'll adjust you as necessary.