If you havent flown an aircraft of significant size and momentum, Id definately recommend spending the time and money to receive some sim instruction. It is after all an investment in your future and you would kick yourself if you failed to gain employment due to a poor sim performance.
I spent quite a few hours flying a heavy jet sim and it was worth every second. Reduced the mystery of the sim assessment and greatly improved my performance ( from a 1 to a 3 out of 10 I might add !!).