Tooter:
To respond a bit more directly to your question: you will not be using "overkill" if you choose a 10 AWG speaker cable, but it may not be necessary to use such a heavy cable. There are two issues here:
1. the length of the speaker cable (from the amp to the speaker);
2. the speaker you are using (full-range speakers with large woofers draw more current, so you may need heavier gauge speaker cable).
For the sake of discussion, you are usually safe with a 14-gauge speaker cable if your cables are 8 feet or less in length. As your cable gets longer, you want to increase the wire gauge. There are no "absolutes" about length vs. gauge, but I usually advise using 12-gauge speaker cable if the amp-to-speaker distance is more than 10 feet, and 10-gauge speaker cable if the amp-to-speaker distance is more than 15 feet.
The actual thickness of the cable (internal wire plus outside wrapping/insulation) can be a potential issue if the cable is so thick it's hard to bend, or so heavy that it causes smaller monitor speakers to become unstable on their stands.
The AWG of the speaker cable is not the only issue, however. With heavier, longer runs of cable, you should pay attention to the electrical characteristics of the cable, particularly resistance and characteristic impedance. There are a number of good speaker cable manufacturers, and it would be a good idea to look at the specifications of the cable before making a final choice. There have been a lot of threads on this topic, so you might want to search the A-gon archives. Try looking under "speaker cable gauge", "recommended speaker cable", or something similar to find the threads.