^^^^
Uhh, triple-post? Delete 2 of those, please.
You guys are all missing one important point: The 6s is easily $6k more than a Mazdaspeed Protege. You really should compare it to the 4-cylinder 6i, which would cost about the same.
My take is, you can get a base 6 for the same as the top-of-the-line Protege. The 6i has more potential because it's not sporty at all to begin with. It doesn't have a sport suspension, big wheels/tires or anything like that. It would be a great platform to build a car on, since it has the 2.3L instead of the Protege's 2.0L, but you could basically re-do the entire suspension, engine, add a turbo, new wheels, tires, interior, stereo, etc. all to get ahead of where the Mazdaspeed Protege starts.