40ft: speaker cable or interconnect?

After reconfiguring my HT my LCR speakers are about 40 feet from my amp (Bryston 5b-st). I used to have 20-25 ft. runs and things sounded good. I used Frank's (Signal Cable) classic speaker cables.

Now that I've added another 15 feet, should I switch over to interconnects and relocate my amp near the speakers? Aesthetically, I prefer not to do this, but if 40 feet of speaker run isn't recommended, I'd consider it. I might also switch over to mono amps if I did this to minimize foot print up front (maybe Nuforce Ref9 or the like.)

Thanks,
John