The question never is how fast do you want to go? Its how much do you want to spend?
I started a project car in 2003. Added a turbo setup to it. It was great for about 3 months. Oh man this is slow, pulled the motor, forged internals, head work, over sized valves, and a cam then cranked the boost from 9psi to 20psi, tuned it. Oh man this is great! 6 months later blew the transmission. Rebuild transmission and put it all back together, this is great! Blew an axle a week later, custom built axles..oh man this is great...then I went oh crap this isn't great, I just bought a 15,000 dollar car, put 20,000 more into it and have a 10,000 dollar used car. This isn't so great.
It sure was funny though driving around in a completely stock looking 2003 Dodge Neon SXT and blowing mustangs off the road like its nothing. Ran 10.93 in the quarter on slicks. To get it into 9s would of been a ton more money, and no longer streetable.
I ended up pulling the motor and putting a junkyard SOHC 2.0 and transmission from a 97 Dodge Neon and stuffed it in there. Then traded the car in on a new truck. I sold the engine, transmission and the entire turbo setup to a guy for 10,000. I lost my butt on that deal, but made more than I would of if I would of traded the car in with all the mods.