The Smart Strider 735 has extra features over the 535. The $200 extra for the adjustable power ramp is well with the money in my opinion.
The Smart Strider series from Proform gives a very good ellipse motion that resembles both Precor and LifeFitness' commercial machines. No other low cost machine on the market gives you this quality of an elliptical motion. The problem with this series is that the warranty service department from Proform is awful. Just understand that if you need warranty support it will be a real headache to get it from Proform.