My situation is almost identical to yours - Droid X, and with the S3 120 dBm to 94 dBm (Droid X was consistently 10 dBm better).I transitioned from a Droid X. The coverage at my house is not great, with the X I typically had 1-2 bars, sometimes 3g, usually not. Never really had issues with data or texting; calls could be spotty.
Edit - the signal strength in my house ranges from -120 dBm to -94 dBm
In the end I chose a Wilson 841263 Antenna which has boosted my reception by about 20 dBm - beyond what I had with the Droid X - no more dropped calls and no more echos of "can you repeat that?" Cost was $350 delivered and I justified it in terms of quality of calls and my sanity. This may not be an option for you, but since out situations were almost identical, I thought I'd share my experience.
The thought of testing / configuring / returning phone after phone and comparing them to the Droid X in hopes of finding one comparable in reception was more than I could cope with.