spending that much on a body is kind of pointless. There are advantages to shooting full-frame...heck medium format or even film. Buying the most expensive camera a company makes only gets you a lighter wallet. I think people forget why they even need the extra pixels and high ISO settings in the first place. The best night photographs are captured using low ISO and the right techniques. You don't need a billion trillion megapixels or ISO 1 billion for that. Just about any DSLR out there can do what you want.

Lenses are where you should really be spending money on. It's a better investment and they tend to hold their value. It's also the most important aspect of your gear. It's what that dictates what your sensor sees. That's not to say a good body isn't a good investment....just don't get caught up in the spec sheet or price. The D810 is a great camera.... but so is the D750, D610 or D7200.

Personally, I'd buy the D610 since it doesn't really hurt to go full frame if you can afford it. If you have more money leftover, buy a really nice zoom lens with a fast, continuous aperture or a bunch of fast prime lenses. I'd also grab the SB-910 speed-light. Comes in handy for indoor low-light shots and you won't need stupid high ISO's. ISO 6400 is plenty if you can't use a flash. Unless you're some wannabe paparazzi or someone shooting a once in lifetime event where for some reason you don't have a fast lens, can't use a flash, can't use a tripod/monopod and the only source of light is a flashlight 200' away, you really don't need to be shooting at that high of an ISO. The majority of my shots...especially the night shots are done at ISO 200 or less and with a longer exposure or with a flash. Once you understand the concepts, you can decide for yourself if its worth spending the extra cash.

Your gear accounts for a 1/4 of what makes for a great image.... and that's being generous. The rest is talent, technique, patience and a little bit of luck. I guarantee you you'll get better shots buying a used DSLR, a 50mm prime and taking 10,000 shots than you ever will buying the most expensive gear the camera store has on display. If you must spend money on the top of the line gear, there's also nothing wrong with refurbished or used gear. Adorama or B&H usually sell them with warranties which takes the worry out of the equation

Renting gear is great if you just need one for a shoot, but not if you're in the market to buy one. Try it in the store and just buy the camera which feels right. Return it if you're not happy. Even if they charge an open box fee, it's still cheaper than renting both cameras. Unless you have a nice lens already, you'll probably have to rent one of those too. That's probably around $150-$200 that could be going towards a piece of gear you're going to own

It's very accurate. My buddy and I was shooting under the bridge the other day. Both of us has aperture wide open at f1.4. He was shooting the D610 and had to use tripod. He was so surprised my image came out sharper than his without the tripod and flash. But then again, my lens is 24mm 1.4 which is superb in the low light too.

If you do decide to go with the D750, however, there is a known issue about unusual flare under the intense lighting condition in the early batch. But Nikon has addressed this issue by adjusting the auto focus unit position.