Here's the issue with 5MP and I've tested a few. There's limits on what current lenses and sensor can do. This applies to all digital cameras. If I take a picture with my 12MP DSLR, I will get an image that has 12 million pixels but that does not mean I will have resolution at different settings that comes close to that. Actually, if you go to a site that reviews digital cameras, you will find 16MP camera that have lower resolution than my 12MP camera. This is measured by a set of lines that converge on a standard test chart. The tighter they get, the more resolution is needed to distinguish between the lines. So in the day, you may see a difference, albeit not 2.5X what a 1080P 2MP camera would show but at night, the difference diminishes quickly. From my personal experience, I have not seen a substantial difference in resolution between typical 3MP cameras and 5MP cameras. If I did, I would be using them.
As for PTZ cameras, Axis does not make a good one. Why, because they haven't yet figured out how to make a plastic dome for them. The P55 series to this date still has a white line near the top of the dome that is very annoying. The Q60 had a similar issue but considering the price, they fixed it, but still not perfect, but better. I had a customer pull out all his Axis Q60 and replace them Dahua and to this date, he will only buy Dahua PTZ and I don't blame him. The build quality and image quality is superior and the price is less than half. Most of them are 1080P (2MP) but they do have some models with 3MP.
If it was me and I needed 5MP, I would get two 1080P or 3MP cameras side by side and end up with 4-6MP. Put side by side, the pixel width would be be much better than a single 5MP, after all, most people need the picture to be wider, and not capture a lot of pretty blue sky or grass.