Over the length of the run, solid core wire does make sense. BloggingITGuy has hit on one issue that crops up, though, and that's termination. That transition point will contribute to the overall resistance of the system, and multistrand wire will likely provide more surface area for crimped connectors or for bare wire into a binding post. How much difference it'll make, I don't know. I could certainly see a case where this proved to be a failure point if something were not quite right, as is of course also true with stranded.