Can you hear me?

When we first downsized our QTH (mistake!) my antenna made its way to the attic.  I settled on running 25 watts for the following reasons:

• Low power was required because the antenna was in the attic and the dwellings are very close together in the neighborhood.
• RFI from my transmitter was not acceptable.
• The old rule of thumb was to hear the difference at the other end it took a 3 db increase.  Therefore, power would have to double for it to make a difference.  Not wanting to go to 50 watts or even higher I would just live at 25 watts.

The third bullet above is starting to be questioned.  If my little 1.5 watt NorCal 40B can be heard (yes even with my attic antenna) would a power increase of less the double make a difference?  This is supported by the fact that I make many contacts at 2 (HW-8), 5 (TR-25) and 10 (FTX-1F) watts.  Maybe just a few watts would pull my signal above the noise level and result in more contacts.

I am now testing for possible negative effects of increasing my power level.  I would like to get to 35 watts with a very remote possibility of getting to 40 watts on certain bands.

Note: RF Exposure calculations performed.