I hope you got some good pix.
I find that the RZ handles just fine hand held. I don't know why people complain so much about it. They make straps for a reason. It has fast shutter speeds for a reason. They made the 110 mm f/2.8 lens for a reason. (The 65mm f/4.0 works great hand held as well). They make fast films for a reason. They make prisms and winders, and all that jazz for a reason (though I usually don't use either; sometimes a borrowed prism). If light is strong, you don't even need fast films. I shoot 100 films with my RZ frequently hand held.
Now, will results be better on a technical level with a tripod? Of course...but that goes for ANY camera. Hand holding the RZ, you get a versatile and stable system SLR platform that will allow you to get fat film frames that you would not be able to get on a tripod. (Otherwise, you'd be using a tripod, right?) If you want to hand hold for 6x7 negs, it is certainly a perfectly fine choice, if not an excellent one. Because it is an SLR, it is certainly faster and more accurate in quick focusing situations than a rangefinder, and because of the design, doesn't shake as much as a Pentax 67 IME (plus it takes backs, which you can preload, allowing you to change to a new roll of film in about 10-12 seconds).