So much for new and improved.
A bit of math in antenna gain, tx power, and rx sensitivity. Rounding off a bit. 12dB is 25% of your range. 6dB is 50% 3dB is 75%1.5dB is 87.5% Therefore, for you 20% loss in range, there is about a 1dB difference between the v1 and v2 incantation. I have no way to tell if it's in receive sensitivity, transmit power, or antenna gain. My guess(tm) would be antenna gain. 1-3 dB variations in product lots are all too common.
Different chipsets have different algorithms for dealing with reflections. If the weak signal is the result of going through walls or floors, you're really measuring how well the receiver can handle multipath. How well does it work in a line of sight and minimal reflective environment?
The v1 to v2 transition suggests a change of vendor so that two cards may be completely different inside. Could I trouble you for the FCC ID numbers so I can look at the inside photos on the FCC web pile?
Ouch. Now, that's bad. When that happens, check whatever utility is supplied with the card for the connection speed. If it has slowed down to 1-2Mbit/sec, then the card and/or it's driver is doing a very bad job of handling interference. They're suppose to slow down or stop in the presence of interference, then speed back up when it goes away. Some drivers do not recover very gracefully. If the speed stays fairly high, then that's not the problem.
What access points or wireless routers were you using? Just curious if you're mixing chipsets.