I was in the same situation as you about 2 years ago upgrading my analog to HD, I got an 8ch Hik NVR with 4 cams, this quickly grew to 8 cams and the problem was I ran out of bandwidth and had to dial down the quality of the cams to meet the bandwidth requirements of the NVR.
I fixed this problem by upgrading to a 16ch NVR giving me twice the bandwidth; I can now run all my cams at full quality without any problems.
I also opted for a non-POE NVR using an external POE switch, this will give you easier access straight to the cams over the network, the NVR will cost less and gives you flexibility for installation. You can mount the switch closer to your cams, I have mine mounted in my crawl space and only run one wire into the house instead of running all 8 from the cams into the house and NVR.
You should be able to get a 16ch non-POE + an external switch for about the same price as the 8ch/8POE that you posted. If your sure 4~6 cams is all you need then the 8ch should do fine but you should leave room for expanding.
Just some other options to consider.