No solutions, sorry. I use both a PS3 and 360 to stream videos off my Mac; and the same video, on the same server, on the same network always plays smoother on the 360. I've heard Ethernet performance is far better, but I only use Wifi (Mac is in a different room with Ethernet not an option).
I bought a new Belkin router, and updated the PS3 firmware around the same time, and one of those seems to have made an improvement, but it's still quite poor for me too.
I'd much prefer to use the PS3 for streaming media (it's so much quieter), but with the poor Wifi performance it's not really an option.