I am an Officer of US Marines, I have attended army schools, (FAOBC and FACCC). While at FACCC I took the APFT (and my Army counter parts in my Plt took the Marine PFT), I normally do around a 245-250 on the Marine PFT, I got a 298 on the Army PFT. Most of my army friends that get in 300+ on the extended scale were in the 275 range on our PFT.
The pull ups are actually a bit tougher to do than the push ups, 20 pulls ups (max score) is a lot harder than the 70 something in my age group for 100 points. The Army sit ups were harder to do than the old Marine sit ups, but a lot easier than doing the 100 crunches. AS long as it wasn't your first time to do the Army sit up you would not have any real problems. All the Marines thought the 2 mile run was a breeze. It is more a test of ability to endure pain than of cardio vascular endurance.
One of the things that really makes the Marine PFT harder is that is it is not adjusted for age, to max the test a 40 year old has to be able to do everything as well as a 18 year old.
Just like in the army you can make all the minimum as fail the PFT. If all you can do is 3, 42 and 28+ you will still fail.