Having spent $40K brand new for the BOSS, I can add quite a few upgrades that will out perform the GT 350 and still not touch that realistic $60K figure. That includes handling as well. The 500 plus HP is easy to obtain with bolt-ons on the Boss.
Says the guy who has no clue about the performance capability of the GT350! With enough money though, you can make any car blisteringly fast. I think it will be harder than you think to bring your Boss (which is an awesome car in its own right, BTW) up to GT350 spec.