The raw truth is that Samsung Galaxy Note series is a class apart from Google Nexus series but this does not stop people from comparing both the devices for certain inevitable reasons. Both rumored to release in October, 2014 will have powerful hardware for sure. However, the exact specifications are not available yet. Based on their previous models and latest available hardware/software, an assumption can be made though.
As usual, Samsung would incorporate the latest hardware and software versions in Galaxy Note 4 whereas Google in an attempt to keep it low priced would take steps accordingly. Note 4 is expected to be available in 5.8 or 5.9 inch Super AMOLED display and believed to have QHD resolution, 1441×2560 pixels. Nexus 6 is expected to come in 5.5 inches or less screen size and have IPS TFT Full HD 1080×1920 pixels.
Galaxy Note 4 would probably have the yet to be released Snapdragon 805 processor. It is expected to come with 3 GB RAM and 16GB/32GB variants of memory storage. Google Nexus 4 is rumored to feature 16GB/32GB memory storage and 2GB RAM with Snapdragon 801 processor.
As far as the cameras of both the devices are concerned, Galaxy Note 4 is going to have the same camera as in Galaxy S5 while Nexus 6 may have 13MP camera. Both the phones are expected to come with more camera features than their predecessors.
If you want a phone with more features then Galaxy Note 4 is surely to go for but if you want a cost-efficient and faster phone then Nexus 6 is to be picked since the latter is less buggy and way faster than the former device.