Thanks. Just a lot of drop setting therein. It wasn't on camera, but I also did 135 for like 30 after the 225 set. I just try to blow myself up essentially. The 300 was done pretty much at the end of a 4 week heavy wave of training, which followed a 3-4 week single set AMRAP scheme. I've used that "formula" for years to get my strict up, or to par. It hasn't let me down yet.
As for assistance, I just usually switch it up between floor pressing and close grip incline. I personally really like standing strict 1-arm dumbbell presses. Truth be told I can't say much in the name of the smaller auxiliary work as they've done me more harm than good it seems.