I vote for the fourth choice.
Pay the car off first. Seriously. I was as guilty as anyone else in terms of spending more than a little money for mods on a car someone else technically owns, but I've waited until the car was paid off before even considering doing any major mods.
Not to be preachy or anything, but unexpected things can happen in life and it would suck to have sunk money into the car that might have been better used to either pay it down or weather a job crisis. BTDT. And if you were/are planning to just go deeper into debt to acquire a power adder, well - no offense, but that's just not smart.
But to answer your question, I'd go for the three liter.
I wouldn't even consider the supercharger since it does nothing for low rpms and has issues on it's own. NOS is out as well due to the ongoing expense and hassle of bottle refills, along with the potential for damage unless you opt for a good controller (more $$$). The turbo looks to be the best bolt on choice, but at a cost of more than half the payoff on your car, that's just not a good idea at this time.
Of course, this is all my poor personal opinion and could just be a bunch of hogwash.
Dan - seriously considering starting on a 3 liter
