Bob... I have driven my Dad's rail. And I drove a Gen 2 Big 5. And a Hustler 4. And a Gen 3 Big 5. And a Gen 4 Big 5. I can tell you this... they all worked very well, handled good, and were just all around great buggies.
But there is a huge difference. My Dad's Funco rides great and jumps great, much better than my own buggy by far. But when I drove Bohica's Gen 4 car I was absolutely amazed. MUCH better. WORLDS better.
Like all builders (or at least, most) Funco has bettered their product year after year. If I remember correctly my parents bought the fifth Big 5 ever produced. Funco has probably sold over 300 of them since (not sure on the exact number), and it's quite obvious they learned from experience how to make them better and better each time.
I better stop now before someone complains that I sound like I work for Funco.