Yes, set a static IP and manually open ports on the router can help some times. As we all know, the online stabilty also depends on the brand of your router.
Some people also claim that messing with the MTU will increase online performance. It can also be problems due to the QoS, and that is what applications should be granted more bandwith (if you have multiple users on your network). Second, if you have IPTV or VOIP, the providers some time locks the latency on a certain level to aviod drops, what ever that means....
Then you should not run wireless, because the network card in the PS3 isnt powerful enough. My experiance, and many others is that the connection gets more stable with a wire.
This whole online issue thing os more complex than most people think.