Reading your post just had me wondering a few things.
just curious on how you arrive at the conclusion that the 15-85 isn`t sharp?
On a cropped body its as sharp as the 24-105L and the 24-70L.
If you are chasing sharpness the 28-75 Tamron delivers better values, especially on a cropped body.
If you look up dxomark and compare lenses the 15-85 has higher resolution figures than the 70-200 2.8 and the 70-200 2.8 L is mark 1 on the same cropped body.
But what does it really matter
Sharpness is only part of the story.
Why do you see yourself getting a ff frame body in the future and will the 550d not be a great second or back up body?
What does the cropped body lack for your needs?
For serious portrait work have a good look at the 85 1.8 usm and 50 1.4 usm. They will deliver now and if and when you upgrade to ff. For a zoom portrait lens consider the tamron 28-75 it is very good on a cropped body and will work on a ff, its a lot cheaper, smaller and lighter than the canon 24-70.
But once you do have a ff body, the 70-200 maybe all you need for portrait work and then you may have a better idea of what lens to buy, in the meantime choose something that best meets your needs right now.
cheap kit upgrade is the tamron 17-50 or 28-75.
or the two efs 15-85 and the 17-55.
or just keep the kit lens and get a couple of primes.