I personally have not tried these ones, but I have tried the Esoteric Audio 14-gauge speaker cables that a lot of places use as their "house-brand" speaker cable at similar prices. The Cambridge cable might be the same. I did a direct A-B comparison between the Esoteric and Monster XP, and I preferred the Monster XP! Seemed a little more open and natural sounding to me. These were relatively short runs of about 8 feet, though. I think XP is a decent value, if you don't need long runs. I personally prefer Monster's "New Monster Cable" -- even over some of Monster's own more expensive cables (like the cheapest M-Series cables, for example, which sound thin and "wiry" by comparison, even at around $60-70 per 10 foot pair).
Avoid "Original Monster Cable" at all costs! It oxidizes very easily and will turn green before you know it. The "New Monster Cable" with its "PEX" layer in the insulation seems to preven this from happening as quick. I've also heard good things about RadioShack's braided "Megacable" but I have no direct experience with it.
If you are on a budget and don't need all 50 feet of cable, I would recommend two 10 foot lengths of "New Monster Cable," which, at $1.50 per foot, would add up to about $30.00. There are, no doubt, people who would disagree with me here and proclaim that (1) all Monster products suck, or (2) that you can do better for the price. They may be right on the second count, but my advice is just based on my own experiences.
