http://www.roadandtrack.com/new-cars...-chevrolet-ss/
Those E39s are awesome...and I really can't see how a new Chevy SS is a FINANCIALLY good move. It's certainly a good car but I'm not sure where you are saving or making money. The SS has not done very well in sales and isn't something that I would expect to appreciate in value so I'll need you to explain why it is a good financial move.
I'd keep the M5 as it is unlikely to depreciate much more and any maintenance certainly can't be as much as a brand new car. That written, the SS seems to be a great car too and if you get it then congrats!
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2016 Camaro 2ss
-Summit White / Ceramic White
-8A, NPP, MRC, Ceramic White package plus knee pads, black bowties.
-1st Car to have the "full" SEMA High Performance Graphics kit from 6LEDesigns.
-1st Car to have the 6LEDesigns Blade Spoiler.
-Borla S-Type w/ custom H-Pipe
-Procharger P-1X Stage 2