For pictures,
What year is her 300c?
I've never been in a 300, but Ive been in a charger and I know that the 300c is a damn good sleeper. The m45 is a sleeper in its own right in that very few people know what it is and even fewer expect it to be as fast as it is.
That being said, the m45 probably won't be as fast off the line due to the Chrysler's torque although the HP is similar. I think the 300 has a better rear end as well. Not sure how the ride quality would compare -> Chrysler 300 = q45, dodge charger = m45. I thought the m45 rides better than an E-class i had, which inspired the earlier Chrysler 300 suspensions.
The m45 is a midsized sedan for all intents and purposes and the rear seats are cramped for tall people. The front seating is quite narrow too. My experience with American cars is that they value space. It is also my assumption that the interior of the m45 will feel better - quality and touch, although the American car might have more features. Remember not too many vehicles came with heated and cooled seats and a sensible voice command system in 2003, like the m45.
The downside of m45 ownership is its rarity. When parts fail they can be difficult to source and expensive to obtain. But it's an old school Nissan, so reliability is pretty good. 300 parts are easier to get and things can be modified for a little cheaper.
But you'll definitely like being in the m45.