There are significant differences between 633 and 635 (all are considered CSis) and the resale pricings reflects this. Mostly the differences are suspension and FI systems and of course cosmetics. I personally think, from owning one for 3 years, the 84 633 is the best deal out there. The pricing on the 633's are 2-3k less and this model year has almost all the features of the 635 and essentially the same FI system (the earlier systems were a little more troublesome). Euro models also tend to be cheaper. Can anyone educate me on this? What is the difference between the 635csi and 633csi? Also between 635csi and regular 635? (I assume those differences also apply to the the 633csi and 633) Thank you and please excuse my ignorance. I trying to buy one of thesse magnificent autos and want the best for my $$$$.