I have a 2 part question: is there anything i can do to boost my ps3 connection download speed as high as it would be if it was connected straight to my modem while using a wired connection to my router? if that's not possible, is there anyway i can keep a stable download speed @ 5mbps?
First, what are you using to test your speed. The speed it gives you during a connection test means almost nothing. Its better to do a test in the PS3 browser (make sure you have the latest PSN update) and pick the same server as the one you did for the computer. That will give you a apples to apples test.
Second, the best thing I have found for performance is to use a static DNS of 8.8.8.8 and 8.8.4.4 . This is google's DNS. Granted, there are other DNS which may or may not work better for you, but it's a good place to start. Having a static DNS helps with how long it takes between boot and signing in, but doesn't do anything for performance. Just make sure you have a DHCP reseverations so any gaming rules/gamefuel rules/etc you put in place apply to the PS3. Also, if your your on DSL try setting your MTU lower. There are complex test you can do to see exactly what your MTU should be, but try it at 1400 and see if its better.
Last, when ever changing any PS3 settings, to a Easy connect first, reboot, then do a manual setup to change the settings. I find with my PS3 slims, if I have a manual connection setup and change a setting, it doesn't apply. I haven't figure out why yet, but I have seen it happen on other's PS3 too.