You need to wire it up. I believe PS3 Skinny also uses wireless G, atleast according to the specs on the amazon product page (along with everything else i've read).
As you've figured out, you would have to have the worlds best conditions to achieve anywhere near the max of 54 mbps , and I can assure you that you will get substantially less than this unless you are in some sort of wireless test bed at one of the larger chipset makers.
I tried to stream wireless 720p/1080p via PS3 media server on my mac, all wireless, and it didn't work. It worked a little but i'd often have to pause it to let it rebuffer, and my guests would often wonder why my awesome setup sucked so bad
The only way I could get the solution to work as it should was to build a Windows 2k8 box and serve it from there (using ps3 media). The entire network is gigabit, wired with Cat6 (won't make a difference, but they were cheap and certified) and now it works great. The server CPU isn't busy doing anything else so I have it on the higher quality settings and it doesn't bat an eye.
With that said, if you really need to be wireless for physical reasons then there are options. The
Linksys Dual-Band Wireless-N Gaming and Video Adapter will join your network as a wireless N device, while you just plug it into the PS3's ethernet port. It ain't cheap though, but it will work.
I don't think wG will have enough bandwidth to stream hd, period. Not an any kind of quality (think web video).
