Rather than hash out things like the the extra body flex of the 'vert vs. lighter weight and familiarity with the e46, etc., in theory.... as you noted, the best answer comes from hard data.
Consider running in an SCCA event. You could enter both cars in different classes. Those suspension mods will bump you up into a classes where there will be some "very" competitive cars...ans well as drivers that are committed to more than 6 weekends a summer. At least you can run both to see which you prefer.
If being competitive is the primary criterion for the decision, then you may be happier picking the faster vehicle. If you do it to learn, then the slower car *may* have more upside, depending on the reason it is slower. For example, a change from junk tires to properly-sized and inflated quality rubber (never mind the real sticky stuff) can shave, literally, seconds on a highly technical course. If you autox to have fun, then the decisions may be based on different criteria.
Have fun and GL.
Last edited by sunsetcoast; 01-22-2013 at 10:40 AM.