Upgrade the 4 or put in a six - it's what the car was designed for.
I bought my car with the intention of doing a suby swap. The more I looked, the more I just could not stomache cutting the front for a radiator. Plus, the more math I did, the more I realized that there really wasn't that much cost difference between any of the alternatives if each of them were done correctly. If you are a great fabricator and/or have most or many of the parts already for one or the other, then the math may be different for you.
Because you already have a Raby kit, that is by far your most cost-effective way into additional hp. I chose a 3.2 6. With a freer flowing exhaust and a rechip, the car should be approximately 240-250hp at the crank and it is right for the car. My 4 will be stored for a future project.
Whatever you decide, do it because that is what you really want. Better to save your nickles and wait than do something less than what you want to get it done. In the long run, you'll be happier with your car. Good luck with your project.