I had just posted a thread not long ago about which was better, darkfighter/starlight or higher res cheaper cameras with external IR illuminators. The vast majority of people said higher res cams with external IR. You will probably want the 850nm IR illuminators which are the brightest from the camera perspective but have a faint red glow at the emitters. You might even consider adding those illuminators first and see how much better your current system performs with them. Once the illuminators are in place you can still replace your current cameras with new ones and the IR illuminators will benefit the new cams as well.
Personally I am a fan of the Dahua cameras. I would probably go with turrets instead of bullets for two reasons, I prefer the separate IR emitter lens so there is no bleeding into the primary cam lens and because you can get turrets with built in microphones. I figure why not add audio to the recording if you can.
These are the models I will be buying once I get around to completing my wiring project so I have the infrastructure to use IP cams:
IPC-HDW4431C-A This is the newer 4MP turret cam with H.265 and a built in mic
IPC-HFW5421E-Z This is a zoom bullet 4MP cam
NVR-4208-4K This is the NVR, it is available in 8ch/16ch/32ch but you can always use fewer channels than it has, plus you can expand into it in the future if you ever wanted to. The NVR does NOT come a hard drive so budget extra for drives, Western Digital Purple seem to be the popular choice for NVRs.
IPC-HFW4421S This is a fixed bullet 4MP cam
SD59430-HN This is a very nice 4MP PTZ with 30x optical zoom (totally not on your list but I thought I would suggest it anyway because.....awesome?)
48 element IR illuminator This is a possible illuminator you could use. Another user on these boards bought both of these illuminators in 2012 and has been happy with them
30 element IR illuminator This is a possible illuminator you could use
The IR illuminators use 12v power connectors, you can use a
PoE injector and a 12v
splitter at the far end to deliver 12v DC on the correct connector to the illuminator using
cat5e/cat6/cat6a. You could also use a PoE switch for the source power to the splitter but if the switch is unmanaged it may not detect the splitter correctly and supply PoE to it. So either use a managed PoE switch that you can force the PoE to active on the port the splitter is connected to or else use the injector, I haven't done enough research on this to be totally sure so be sure to check this before investing.
I realize this isn't exactly what you were asking for but you did ask for opinions and I think if you expanded your scope to include devices like the ones I linked you might be very happy with the results. As you can see from my post count I am not an expert so I would suggest you use my post as a rough guide instead of an exact recipe.