On a scale of one to ten how would you rate.......

it would depend on the brand

there is not necessarily a difference in quality of the sonic presentation between an interconnect with RCA vs. XLR terminations. The only difference is that the XLRs will typically give you a 6db gain over the RCAs, so at the same volume level, the XLRs will sound louder. So the difference in sonics will depend from IC to IC based on material used in cable, cable design/geometry, cable shielding etc...Only way to tell is to try out various options in your system.

I know that everybody suggests when you do long runs (very long) you should be going balanced. Surely this isn't just to get that 6db of gain, isn't there more to it than just gain. Some manufacturers suggest that sound quality will be better when going balanced. Not disagreeing, just throwing that out there.