You can't say both though. You can say he isn't fast enough to be a WR and not big enough to be a TE but you can also say he is bigger than the average NFL WR and faster than the average NFL TE.
Facts are, we won't know Postma's speed until the scouts come to Houston for pro day. There is a difference between measured speed and speed with the ball as well. We have witnessed that Postma has plenty of speed with the ball. It's almost become a reverse discrimination with him from the fans and the media. I heard the announcers say that King is a dual threat, so he brings more to the table than Postma and Allen.
What we saw out there, Postma didn't lose his job because of any lack of running ability. He lost the job because he made too many bad throws.
I think Postma needs to be out there in the same capacity that King was out there. Not just for Postma to have a future with the NFL, but because that gives King the same playbook to work with that Postma had. Instead of playing Postma as a wideout in formations like King, let him line up as an H-back IF he doesn't have true wideout speed but I'm willing to bet that Postma is middle of the pack speed compared to the two-deep chart of our wideouts.