If this knife is going to be for hard use you need to take into account a few things. How easy will the steel be to sharpen? At over 6" it might take awhile. Edge retention is another factor. If its hard use you'll be using the knife for, then chances are that you'll be in harsh environments. Are you concerned with corrosion? These are some factors to think about when choosing steel.
Personally, based on the size of the blade and the intended use, I would use CPM 3V or CPM M-4. You won't find a steel tougher than 3V. It's edge holding is very good as well. It is amazing how durable this steel is. Most 3V blades do have some coating or finish on them. Try an ferric acid etch.
CPM M-4 is also very tough but excels at edge holding. I guess it really depends on if the hard use will be chopping or cutting. You really can't go wrong with either. Price might decide for you though. CPM specialty tool steels are fairly expensive but will make an excellent knife.