The Mk 16 is discontinued. No big deal, it will be supported for decades, but it does mean the dealer can discount it all the way down to his cost.
The Mk 16 is a fine reg that formed the basis of the Mk 17. The differences are that the Mk 17 is sealed, has an extra HP port (one on each side) and has an improved seat alignment system that is retrofitted into the Mk 16 anyway.
The main difference is the R190 versus the G250V. The G250V is phenomenal and the R190 is just another unbalanced entry level second stage. The real performance difference will show up there as the R190 will not breathe nearly as well as the G250V.
As an aside, the SP dealer can do a heavy discount on any second stage sold with the discontinued Mk 16, so ask what he would charge in addition to upgrade you to a Mk 16 G250V in that same package.