But if you want one of the quietest and biggest cabin class twins ever made, this is the one
AdamF,
Sounds like you do not have much experience with the actual aircraft, or the engines.
At least they speeded the development of the 690 --- the basic airframe really needed the extra HP the Garrets provided. As a good mate of mine, with a large part of his career bound up with various Aero Commanders will tell you for free: "Most spectacularly underpowered aircraft I ever operated".
Tootle pip!!