wifi connection can be dependant on a number of variables, one of which being th distance from the router and how many/how thick the walls are too.
i tend to keep my ps3 lay face down, with (what would be the bottom of the ps3 if it was stood up right) facing the wall which the router is behind, and that gives 100% signal.
Im sure there are some tuts on here for increasing the signal strength, but you'll have to search for them
a slow connection shouldn't mean that you recieve a bad signal.
the best advice i can give you is to try your ps3 in all different kinds of positions until you find a reasonable signal, and if absolutely all else fails... buy an extremely long ethernet cable