While the 4-Max is definitely a good and durable folder (once it finally hits the market), it isn't like you're realistically going to beat on an American Lawman or an Ultimate Hunter hard enough to ever really cause severe damage to the knife, unless you're trying VERY hard to do so.
CTS-XHP is an awesome all-around steel, and while 20CV will usually have higher edge retention, at the thickness that it will likely end up behind the edge on the 4-Max, you're not liekly to really see any higher edge retention from it over regular CTS-XHP. So basically, what you will likely end up with is a steel that doesn't really hold an edge much longer without being re-profiled, which is a little harder to sharpen than CTS-XHP, and has about the same toughness really.
Frankly, I would just save the money and go with the American Lawman, the AK-47, or the Ultimate Hunter, in CTS-XHP, and then beat the living crap out of it to your heart's content. The steel will be adequately tough for whatever tasks you need it to do, and it will still be easy enough to sharpen back up if you do manage to chip it or roll the edge.
Trust me, I love high edge-retention steel as much as the next guy, trust me, and I have messed with as many of them as I can, but the truth of the matter sometimes is that if you want a truly tough folder, you are probably going to have to make at least some compromise in the edge retention in order for the steel to be tough enough to handle a true beating, and still be easy enough to sharpen if/when you do manage to mangle the edge on accident.
Just my $0.02, but I would highly recommend NOT making your beater knife cost much more than $100, so that if you somehow ever DO manage to kill it, a replacement is easy to find and not going to break the bank.