I did some quick testing. My router is an ASUS RT-N56U.
- The Xperia SP (XSP from now on) is unable to see my neighbouring access points well. Eg. At 1 location, I can pickup about 5-6 on my Samsung Galaxy S3 (SGS3), while the Xperia only shows 1-2.
- The XSP displays the WIFI signal strength on the notification bar differently from the SGS3. Eg. At -78dB on both sets (using "Wifi Analyser" app, SGS3 may show 3/4 bars, while XSP shows 1/4 bars.
- At a location in the house far away from the router, the XSP is unable to even ping the router, even though the icon shows that it's still connected to WIFI, albeit at 0/4 bars. The SGS3 is still able to ping and run speedtest without problems. Testing at this location was done with both phones on a plastic chair - when I picked up the XSP with one hand, WIFI totally dropped (icon disappeared).
So even after taking point 2 into consideration, the XSP's WIFI is definitely not as stable nor sensitive as the SGS3. It might be a problem depending on the size and stories of the house.
And becoz of point 2, let's use quantified values from WIFI analyser app if we want to compare numbers between different phones.