"Good choice on the high-flow cat, OP. One thing to keep in mind, is that a large tailpipe really isn't needed. As the exhaust gases go through the cat and muffler they cool and contract, and lose volume. The 2" pipe is fine, as it will keep the exhaust gas velocity up, along with the torque."
Actually, the temperature across the cat will increase substantially. For a 4 cyl Ranger, you will be fine with 2.25. Crush bending, (as nearly all muffler shops use) will decrease the internal diameter of the pipe when bending, so give yourself some "breathing room", so stay away from 2" or smaller. Now, if you get the mandrel bent system from Magnaflow, (http://www.thepartsbin.com/sitemap/ford~exhaust_system~parts.html) a 2" is fine. Actually, that 115.00 price is pretty good, but I hate doing exhaust. That is just one of those things that the shops can do better than the average Joe, with their lifts and torches.