What I have discovered about APX 400 is that it accumulates base fog really fast past expiration, especially if it hasn't been cold stored. But if you have a strong enlarger light source you'll print right through it, so not much to worry about there.
Just put a roll through to see where you're at exposure wise, and use the other four if your find no major issues.
That is my experience too with every 400 film I've used. You will also probably see a bit of increase in grain. Still it should not show any major issues if stored reasonably well.