40ft: speaker cable or interconnect?

Mogami and Canare are two of the best sounding budget and DIY options. Lots of places will build them to desired length w/your choice of termination.
Frank can certainly make you Signal Cables within your budget.
If you switch amps, going to balanced configuration is worth serious consideration. Balanced longer runs are quieter if the gear is truly balanced. Not all gear w/XLR connections is really balanced, but that's a story for another thread. Cheers,
Spencer

I think you're better off with a 40' interconnect, which should be balanced if possible.

If you have balanced circuitry go for the long IC. If you have ordinary RCA then stick with the longer speaker cable.

I don't think it is worth replacing a bunch of equipment for the sake of 15 extra feet of speaker wire. You could try a blind test (with a friend) to prove to yourself what is very likely; the effect will be inaudible.

I agree with Ghostrider.
I am using Nordost Valhalla, 30 ft runs, and am very satisfied with the results (although not a cheap solution here ....).

While my amp is balanced (Bryston 5B-ST) I'm driving it from a Denon 3806 receiver (obviously unbalanced.) I went through a bunch of gear including Outlaw 990, Halo C2, Sherbourne 7/2100A and Gemstone to arrive where I am now. I wanted a good sounding setup while the whole HDMI thing gets settled. Therfore, using balanced would required some new gear (pre/pro and amp for the other channels.)

I've compared the cost between Frank's Analog 2 interconnect and the Basic speaker cable. "Frankly" (couldn't resist) its a wash....the cost is about the same. I'm sure you could spend more in either application if you wanted to.

Thanks for the input so far!!! :-)