After thinking about it, I think he has found a very good setup for what HE does. I'm kinda in the same boat. My D300 DX camera and lenses work AMAZINGLY for what I do 99% of the time. However put me in a competition in night sports photography or in a studio environment or something that requires 20x30" prints and all of a sudden I'm in trouble.
Recently had that situation. Long story short needed super awesome photos in crazy light situations for crazy large prints. Rented a D4 (really wanted a D800 but couldn't get one) and that solved the problem. Lets see what this client does, if they need this on a quarterly basis then having FX equipment in house makes more sense then renting (if nothing else it sucks big time to try and book it across town to return equipment for a weekend rental, also no time to familiarize myself with the equipment which is ALWAYS a must). However if its twice a year or less, then forget it I'll just stick with my current setup and rent equipment when I need it.