There must be a misunderstanding. When I first bought my DIR-628(at a liquidator), I thought WOW! what a steal. Without doing any research, I had some buyer's remorse, but I toughed it out. I found out that the LAN speed is only 10/100 Mbps, which translates to only 12.5 MBps theoretically. In my experience, I've been able to get about 80% percent or 10 MBps constantly. If you wanted Gigabit speed then this is what needs to happen:
laptop needs wifi N: 37.5MBps theoretical maximum throughput
gigabit router wifi N: 125.0MBps theoretical maximum throughput
desktop needs gigabit N: 125.0MBps theoretical maximum throughput
From what I've learned in fundamentals, all components needs to have a lowest common denominator. So in this example, you've would only achieve 37.5MBps theoretically maximum throughput. But with your setup it doesn't matter if you've got all Cat6 cable (believe me, I've tried what you're doing.I also have all Cat6 cables.) you'll get only the lowest common denominator between them. Here it is:
your laptop: wifi N: 37.5 MBps theoretical maximum throughput
DIR-628(non gigabit router): 12.5 MBps theoretical maximum throughput
your desktop : 125.0 MBps theoretical maximum throughput
So in your situation it will only achieve 12.5 MBps theoretical maximum throughput
I'm sorry if this seems to be the long answer. But to give you the short answer, yes you are correct the DIR-628 isn't a gigabit router. To solve your problem, I suggest getting the DLink DIR-655. It is advertised as a gigabit router. You should get must faster transfer speeds.
I hope this helps:)
By the way, if I am wrong in any way please someone correct me. Thanks!