My advice to the OP is if you have the money to upgrade to a XFI, do so. It is a better unit bar none. But, I have run my Classic FAST for years and have not had one problem. There is no down side to the Classic FAST. My car drives (like a stock GN, even with my big injectors) and performs flawlessly with this unit in my car. One day I probably will upgrade to the XFI because at my cars level, there are alot more features that can be fine tuned with the XFI. At your level, the benefits are less, with smaller injectors etc.
If I was you I would get in contact with the Cal Hartline. There is nobody better to assist you in your needs, and he will not steer you in the wrong direction to make a sale. I trust this guy whole heartedly. His has had multiple opportunities to sale me something I didn't need, but was always up front, gave me options, along with his choice based on my budget and went from there. If you go through him to buy a new or used unit, you will also receive something far greater then the unit you buy, you would receive his customer support and start up tune that will get you started. IMO, the buck starts and stops with Cal where these engine managements are concerned. You would be losing out if you went any other way.............. Just my 2 cents.