Hi Joel,
If you shoot HD with a proper HD Camera, you should use an HD Monitor in the field. Why cutting on a control instrument, which gives you control over focus and colour, which I assume are important features? If you change lenses for examle, you need a proper HD SDI link for check on focus. I would definitely go for an HD monitoring. The workflow you have experienced, sounds good, but is probabla down to a lot of testing beforehand.
Two things:
If you have got time, experience and testing performance, you can save some bucks.
If your field conditions get worse or you haven’t got time it’s silly to experiment.
Rainer