[RPM]

And to add to Bruce's post, you have to consider the parts availability when you are purchasing a gray market bike as well as warranty issues. American Lifan pays for parts and labor for 6 months, most other gray market bikes that I have seen are usually 30/60/90 days - parts only. With an American Lifan, you will have parts, even for discontinued models, in most cases. What I have found in the market is that many times you order a part for your particular bike through whatever means, be it a dealer, catalog or on-line, you will get a part that will fit, but is a little different and may very well require some modifications to get it to work. I know this first hand as most dealers will tell you.
Most of the plastics are hard and brittle on the cheaper models, again in reference to the specs that any manufacturer requests to lower the cost as Bruce pointed out. You may very well see differences in the frame construction as well.
To be one of the biggest export companies in China, as Lifan is, they have to build a unit as they are asked to do for their customer's dollars. The only thing that they may change as far as engines go, is they may change the covers to reflect a different logo or name.