How important is signal strength ?

hi

I am experiencing a drop in signal strength after upgrading my old Linksys BEFW11S4 router / wmp11 pci card 801.11b network to WRT54GS v6 router / WMP54GS 801.11g.

It used to run at good - excellent consistently.

Now it's good at best (usually low).

As far as I can tell, the actual connection capacity seems to be OK - XP SP2 downloads at around 440kbs.

The connection speed (as seen when hovering over the windows network icon in system tray) is usually 54 Mbps, but signal strength is "low".

Firstly, what is the relationship between the signal strength & the actual realworld performance of the wireless internet connection ?

Secondly, would high gain antennae make much difference here (the router is actually in a separate building (outside garage) from the main PC) ?

Secondly, why would an "upgrade" cause such a big drop in signal strength ? It was just a straight swap of hardware, no change in physical location.

thanks

swayzak