yeah Dave ... I was thinking the same thing - 10ga as a minimum.
8ga wire is rated at 40 amps .... the max the CVO generators/alternators will churn is 45 amps. I was concerned about your installing wire (and fused) that allows the potential for overloading the charging system. I ran 10ga wire and have my amps fused at 20 just to see if they blow. They haven't yet. I'll drop them to 15 and see what happens. Since I have 2 amps if they blow at 15 then I'm pulling somewhere between 30 - 40 amps total. Starting to scratch the surface of what the bike can produce.
I "think" the Rockfords will be "ok" at 15 amps (fused) but cannot find definitive info on it - ergo - time to spend some money at the "Shack" to test by blowing fuses 
No performance gain/loss by running 8ga over 10ga over 4ga over 2ga ... well ... you see the pattern
However, the strand count of whatever you install is important. Electrons travel on the "outside" of a conductor - the more "outsides" you can provide the better. A 3000 strand 10ga wire (no ... I don't know of any ... illustration purposes only
) will provide cleaner current than a 4ga solid copper wire. A good "strand-count" for power/ground wire is important - not to mention it aids with install due to the natural flexiblity of a high strand-count cable.
Additionally, the stock speaker wire is more than sufficient for anything the bike can produce. Kudos for replacing it, but it isn't needed (again - just my opinion).
Actually, I did have to replace the stock speaker wire because the stock lower speaker was a single mid-range, and I replaced them with 2-way coaxials (with crossovers with 2 separate terminals to each tweeter and midrange horn). Could have used the 2 stock wires and add 2 more, but I had to change out the weatherpack connector anyway to a 4-terminal so I wouldn't have 2 separate connectors up top. Plus, on the amp end, I couldn't use the stock harness without tearing into it and separating out the wires to run to the new amp (the way I saw it). It was just easier for me to make the new harnesses and run direct from the weatherpacks to the amp outputs.
Thanks for the info...I didn't realize the CVO alternator maxed out at 45 amps (I should have known that though). Like you, I'll fuse it at 20A and see what happens. Might be an issue if I'm running the stereo and 2 sets of heated gear (gloves and jacket liners). Each jacket is 6.5 amps, and the gloves are about 2.5 amps each pair, for a total of 18 amps. Not sure what the lights draw, but I'm also running a powered J&M hidden antenna and Garmin Zumo 665 w/ XM. Looks like a 20A fuse should be the max I should run.
At the moment, I'm concerned the Polk speakers may have not been the best choice because they are 2.7 ohms impedance each. The JL amp delivers 100 watts RMS/ch at 2 ohms and 75 watts/ch at 4 ohms (4 channels). I know power isn't linear, but assuming it is, the amp is delivering 87.5 watts/ch to the Polks at 3 ohms. 87.5 x 4 = 350 watts delivered by the amp. Using Crutchfield's formula to estimate max current draw: 350 x 2 = 750 watts total assuming a 50% efficient amp. 750 watts/13.8 v = 54 amps of max current draw. If I used 4 ohm speakers, at the JL amp's 75 watts/CH RMS, max current draw would be about 43.5 amps...very close to max alternator output. Do you agree with these numbers?
When you used a 20A fuse, did you crank it?? Please let me know what happens with the 15's. I may try those as well.
Thanks again for all the info. I think you just saved me from some future major headaches...