My current DD/trackday/auto-x car is my 2004 330i ZHP. These days it rarely gets any DD time, just occasional trackdays. I bought it in 2010 after the birth of our first child, when a 2dr coupe was just not a viable option anymore. It replaced a 2000 Mitsubishi Eclipse GT (no great shakes). Since then, it served admirably as a daily driver through our first two kids, a couple auto-x events, and about a dozen or so trackdays. With the birth of our third child two years ago, it has been largely relegated to driveway duties. The daily driver is now a 2011 535i, which I mostly dislike in every way when compared to the e46.

All of that preamble to get to the fact that I don't really need to use the e46 for trackdays anymore. I could switch to something else, it doesn't need to be a sedan. I have done about all I can cheaply do to my e46 - intake, headers, exhaust, LSD, dyno tune, under drive pulleys. If the clutch dies I will probably go for a lightweight flywheel. But other enhancements are $$$ (turbo/supercharger, coilovers, carbon, etc). Ideally, I would find something that is capable on track, but also swallows three car seats across the back so I could go back to one car, but that is pretty much a pipe dream.

So looking for thoughts and opinions on other BMW options. Hopefully with some direct experience for comparison. I figure the possibilities are a 135i, 135M, e46 M3, e39 M5, e9X 335i, Z3 coupe/M coupe. Basically, I am looking for something reasonably priced (<$30k?), rear wheel drive, manual transmission, easily trackday capable. I would keep the car street legal and comfortable, as I don't have a tow vehicle or the inclination.

135i/1325M - I know these are every bit as nimble as the e46, and will kick my ass in a straight line

e46 M3 - These still carry a bit of a price premium, but I like my e46. It really is the ultimate driving machine.

e39 M5 - I know this probably isn't the greatest trackday ride. My brother uses his 2005 CTS-V, so that is probably part of the fascination. Plus my desire to get in three carseats, which I realize is probably hopeless.

e9X 335i - Hopefully just as fun to drive as my e46, plus much more poke down the straights.

Z3 coupe/M coupe - Always loved these. But the regular Z3 coupe probably is no faster than what I have, and an M coupe carries a price premium.

I realize there are many other non-BMW options, not covered here.

Thought?