I'm unclear what the "date bug" referred to is - I'd be interested to hear what that is. If it's not in the GPS, this won't affect it, as the firmware talked about here is GPS firmware only. If it is in the GPS, I'd like to see if I can find it in other SiRF based GPSes.
The version numbers sound right for fairly recent GSW2 (standard SiRF) firmware (though apparently not quite as recent as that in my Clip On) and SiRF XTrac II firmware respectively. Be aware that there's advantages and disadvantages in making the change - especially as it sounds as if there's no way of going from XTrac back to GSW2 with the available files.
GSW2 has SBAS (WAAS / EGNOS etc.) support - XTrac II does not. It is true that XTrac tends to be able to get usable signals from more satellites, and can fix faster - but some have reported problems with it at walking speeds with XTrac II (XTrac 1 had lag problems in car, which don't appear to be in XTrac II).
It looks as if the firmware file may not be available any longer anyway.