Welcome to OPF and even more as we need to collect more Nikon users! What a great new camera the D3 is! Now you guys have maybe the best camera for low light club work! I see you do music photography so with the 50mm 1.2 and the D3, I'd be one step higher to digital Nirvana.
I know nothing about the sensitivity of your Nikon camera!!
I just want to greet you and say I like your pictures. I wonder if you create the clouds in some of your pictures. One snow scene made me think that you draw your clouds?
BTW, If you have the money, a great way to do IR is to simply get someone's used camera and have the IR blocking filter removed
here or by a similar company. The main advantage I see is that one does not need tripods. That freedom is a major advantage and easily is worth the $300 or so for the conversion!
I'm not sure if the D200 or D300 can be modified to register the infra-red, but I do know they won't do it without modification.
Also, the D300 is a DX format, which means an APS-C sized (non-full-frame) sensor. Nikon uses the FX designation to indicate full-frame (which right now is just the D3).