Ok, I'm back.
First thing. As I said before, might want to check your Trace log for the speed your rendering device is connecting at. Here's the end of mine:
INFO 2013-06-11 02:08:31.563 [main] Using the following UUID configured in PMS.conf: 4622cf16-664c-3731-8d47-dfa87bb7c47b
INFO 2013-06-11 02:08:31.735 [New I/O server worker #1-1] No IP filter specified, access granted to /192.168.9.100
INFO 2013-06-11 02:08:31.735 [pool-7-thread-1] Checking IP: 192.168.9.100 for Sony Blu-ray
INFO 2013-06-11 02:08:31.828 [main] The server should now appear on your renderer
INFO 2013-06-11 02:08:32.343 [New I/O server worker #1-8] No IP filter specified, access granted to /192.168.9.102
INFO 2013-06-11 02:08:32.343 [New I/O server worker #1-8] Another renderer like Sony Blu-ray was found!
INFO 2013-06-11 02:08:32.343 [pool-7-thread-2] Checking IP: 192.168.9.102 for Sony Blu-ray
INFO 2013-06-11 02:08:36.449 [pool-7-thread-1] Renderer Sony Blu-ray found on this address: 192.168.9.100
INFO 2013-06-11 02:08:37.198 [pool-7-thread-2] Renderer Sony Blu-ray found on this address: 192.168.9.102
INFO 2013-06-11 02:08:38.462 [pool-7-thread-1] Address /192.168.9.100 has an estimated network speed of: 85 Mb/s
INFO 2013-06-11 02:08:39.211 [pool-7-thread-2] Address /192.168.9.102 has an estimated network speed of: 23 Mb/s
INFO 2013-06-11 02:09:02.907 [UPNPHelper] No IP filter specified, access granted to /192.168.9.254
I use PS3 Media Server to two blu-ray players in my house. One is wired to the router, as is my PC, so they can connect at 85 mbps. The second blu-ray player is connecting via wireless in another room. The network speed is fairly low (23 mbps) because my router is an old 802.11g-based router, also my PC tower is sitting in-line between the router and the second player, so the steel case may be interfering (I really should do something about that). I honestly think real-world performance is closer to 15-18 mbps with that player. I have issues with streaming HD stuff on it if it needs to be transcoded.
If you have any metal shelves under your router between it and the equipment downstairs, move the router somewhere else. Same with if you have your PS3 or computer in some cubbyhole with stereo speakers on the shelves above and crap, that will mess with your network connection.
Also, check about other wireless networks around you. If your neighbors are all running their wi-fi routers on the same channel as yours, it's gonna effect your wireless speed. You can use an online tool like Wi-fi Stumbler
to check that if you don't have a utility already on your PC that tells you the channels of the wireless networks around you. If there's other networks on the same channel as you, try changing your
wireless router to use a different channel. This isn't hard, and again, if you don't know how and got your wireless router from your internet provider, call their tech support line for help. Try to move your network at least two channels away from other peoples'. So if you're on channel 11 and there are other folks on it, try channel 9 or 8 for example. Channels 1, 6, and 11 will be the most crowded, because almost all routers ship from the factory programmed for one of these three channels and most people are too lazy/dumb to change theirs. If you change your router's wireless settings after saving your changes make sure to reboot it (unplug the power for 30 seconds on it) to make sure your wireless is operating on the new channel and not in some half-assed betweenville state. All your wireless stuff should be able to reconnect to it without you having to change the settings on them.
After you've tried some of this stuff relaunch PS3MS and see if you got better results. That may fix your problem right there.
You're asking for settings for a low bandwidth connection. Have you tried the choices you have? The settings are actually on a pop-up menu with other choices for lower quality/bandwidth or running on a slower PC:
Try the "Medium Quality for HD Wifi" choice and see if it works better.
Also, last ditch but there is also the scaler:
I've never used it myself, but scaling the image down to an SD resolution would still allow it to be seen even if it's not as sharp, and the smaller image would take up a much lower bandwidth.
Might also consider lowering audio settings. Like setting it to only do 2 channels maximum and lowering it to 224 kbps. If you don't have a 5.1 speaker system hooked up you can't hear the 5.1 channels separately anyway, and the lower audio bandwidth means more room for video in a cramped space.
Remember that if you make changes to your config you need to save them and restart PS3MS
before they'll take effect.