I recently sent my JVC RS20 in to correct a problem with the lens shift mechanism.  When the projector was returned it noted that the optical engine was upgraded.  After installing and testing this unit it now performs like an RS35.  It is much sharper than before, has near perfect color uniformity and the on/off contrast is now 115,000:1.  The motion problems of an RS20 are also corrected in this projector.  The software in the projector is still the same as the RS20 and the settings in the user menu are the same as when I sent it in.

It seems that JVC is not replacing the optical engines with the old versions at this point.