For base sculpting, Silo 2 is a real killer. But it's not capable to do very fine details like Mudbox and it has no layers (but it does store the displacement individually on each smoothing level similar to Hexagon).
I have zero experience with modeling for games. But it sounds like normal mapping is the way to go if games are your target. Modo 202 can bake a normal map from a sculpted high-poly mesh onto the UV's of a low-poly mesh. In fact, the high-res mesh doesn't need to have UV's at all
!!!You only need Uv's on the low-poly target. Watch this video here called "Object Baking" to see what i mean... Layered sculpting is going to be a feature of Modo in the near future. So if you're not in a rush to buy Mudbox, then you may wait a bit to see how Modo develops.
http://www.luxology.com/whatismodo/model.aspx
I believe Mudbox can also bake normal maps in a similar way, but not 100% sure about that. You should post on the Mudbox forums. Or start a new thread here at Polyloop with that specific topic. Maybe you will get the answer you need.
Also, to render normal maps in Carrara, you have to buy the "Deeper" plug-in from Inagoni. It can be found here:
http://www.inagoni.com/content.php?content.2
i hope this helps in some way...
shorty