Without knowing the exact performance of the RS antenna I can't tell you what the difference will be either. Here is the published spec. sheet for the HD7698P:
http://www.winegard.com/kbase/upload/HD7698P.pdf. Currently, the HD7698P offers the highest gain performance available in a combination h-VHF/UHF antenna.
Most SoCal attics get way too hot for any active electronics. If you use any amplifier, I think it best to protect it from extreme heat. A Channel Master CM-3414 or CM-3418 depending on the number output ports needed would be my suggestion.
In the analog days, a signal from an attic mounted antenna would be a bit 'snowier' and have a bit more 'ghosting' but you'd be able to watch it without pixelation or complete loss of signal. The 'cost' of digital TV's 'perfect' picture is that once the signal is too weak or there's too much interference, the picture on the screen goes from 'perfect' to gone as if a switch had been flipped. If we were neighbors, You'd see an antenna or two on my roof.