I saw you mentioned gigabit nics.. should u be using wireless at all with this setup..
Using the DIR-655 for
Wireless HD streaming is not that great as it wasn't really designed for that purpose. Yes, theoretically the bandwidth is there, but in practice it doesn't work well.
For example, it's highly likely that as the action on the screen increases, so do the skips. This is due to the quickly changing demand for large amounts of bandwidth. It's possible for HD video to go from 3mbps to over 68mbps within a 3-5 frame range of video playback.
If there are any competing 802.11 devices within range of the 655, that will also eat into the its ability to provide large amounts of bandwidth.
Now if you had the DIR-855, which uses the 2.4ghz & 5ghz channels, then you're talking about reliable HD streaming. Naturally you'd need to have the appropriate WNICs for that (DWA-556 and/or DWA-160). The Intel 4965 & 5xxx series Wireless-N WNICs also support the 855 fully if you have a laptop.
To give you a real-world example of my experience, I live in New York City.. Wireless Routers everywhere. But my PS3 sits 3' away from the DIR-655. I know the PS3 is wireless-G, but hear me out. I wasn't able to stream even a DVD or DivX video without it skipping. So I tried using my laptop with the DWA-652 WNIC to stream the video from 6' away. DVD-quality was fine. HD video is an impossibility. Works when motion is slow, then skips a lot when motions speeds up.. wash, rinse, repeat. Didn't matter if it was a HD .wmv or a transcoded Blu-Ray disc.
Now that you've your investment in the 655 and associated hardware, you're best of going wired if possible. Wired will work, guaranteed. Since I wired my PS3, it has never had any trouble streaming even Blu-Ray discs from my NAS. I'm more impressed with the NAS being able to keep up than the 655.

If you want
wireless HD, take it all back and get the DIR-855 and the appropriate WNIC: DWA-556 and/or DWA-160.
Having said that-- you may want to check to see what the MTU setting is for your NICs. If *all* (and I can't emphasize "ALL" enough) support jumbo frames, find out the largest possible setting and change the MTU of your NICs in the windows device manager. The DIR-655 supports jumbo frames as of .. guessing .. the 1.2x series firmware, maybe earlier. Make sure you have the most up-to-date firmware.
Also, check out the Advanced -> QoS engine in the web config and disable it, see if it improves performance. If you're not using WISH, you can leave that setting alone.