I'm not sure I agree with your numbers there. Besides which, there's quite a difference between acute doses of radiation and environmental exposure. And comparisons between terrestrial organisms (where I admit mammals generally don't seem to come off very well) aren't the point. You want to be looking as possible non-terrestrial environments, and quite a lot of those have lower background radiation levels than Earth. Gas giants seem to have enormous amounts of radiation shielding, for example. It doesn't seem an unreasonable assumption that life evolving on planets with little background radiation wouldn't have any great degree of tolerance.
@MattII: I don't have screenies for either game, I'm afraid - I haven't had them installed for a while.
Wikipedia describes the different options rather well, and
http://www.starsfaq.com/articles/basic_race_design.htm goes into the advanced techniques.
Basically, you get to set width and position of sliders on 3 habitability ranges determining what proportion of the galaxy's planets are initially habitable. You set a primary racial trait, which affects your overall play style quite strongly. A series of minor racial traits are available, which add perks with corresponding disadvantages. You also configure racial productivity settings (for both population and factories) and how effectively you can research.