Tom, I have a client with a number of driveways where we are using 5MP cameras at distances of 80 ft to 120 ft and capturing license plate images. We had three situations where we couldn't get clear plate data.
Angle of Plate
If the car is turned so the plate is at a 45° angle to the camera at the farthest distance, it could be hard to distinguish some plates. But pretty much straight on, there wasn't a problem.
We did have an issue initially where the installer focused the cameras in bright daylight (long depth of field) and then in low light conditions (short depth of field) we discovered that the focal point was not where it should have been, and plates in the target zone were very fuzzy. Refocusing the cameras during low light conditions and with a plate in the target area, we were able to get the best results and more than acceptable.
When the vehicles were moving at 45 MPH past some of the fields of view, we got motion blur on some images, but could still make out the plate numbers when we looked at them at full resolution on screen.
Of course, when we had 4 viewing windows up at once on the monitor, it could be hard to distinguish plate numbers due to the image downsizing. But viewing the image at full resolution and centering on the plate, the plate numbers were big and clear.
The monitor has little impact on the outcome of viewing an image. The camera has (if setup properly) captured more pixels than any common monitor can display. So, you're going to need to do some kind of software zooming in order to see pixels at a 1:1 ratio (note, that sometimes zooming beyond 1:1 can yield a little more detail, but "software zoom" cannot create or show data that was never captured by the camera). Many people misunderstand "digital zoom". With modern megapixel cameras you're frequently looking at a stream that has less details than what the camera is capable of because the camera resolution exceeds the monitor resolution. Therefore the image stream is downsized in order to fit on the screen. A software zoom let's you be selective about what part of the image stream you want to see, so that way instead of throwing away data universally across the entire image you're throwing away data selectively (just the pixels you don't want to see). You can often times go even further by zooming in to the point that a single pixel becomes represented by 4 pixels, or 9 pixels, or so on. Sometimes this artificial zoom can help enhance the edges of things, or make smaller items larger and more recognizable. Different software platforms could also handle this in different ways, applying their own sharpening techniques. At this stage it is neither the camera/recorder or the monitor working on the image, it the viewing software. Provided your monitor did not come from a thrift shop 8 years ago, changing the monitor probably won't effect the amount of detail you are seeing in the image.
Tom, I doubt it as long as they are digitally zooming into the image and the monitor isn't terrible (i.e., ten years old, beat up, etc.)
Capturing license plates details is a huge pain. You may need to go the route of using image enhancement software but even that is no guarantees.