What is your goal?
You want to look like a marathon runner, more reps less weight. (run Forest run)
You want to look like a sprinter, less reps more weight. (sprint balls out til muscle failure)
If you are doing crunches, for real, stop.
Loaded abdominal exercises are the way to go if you are wanting a not only stronger, but a more defined midsection. If you want to just be able to do a bunch of sit ups and whatnot, just keep doing what you are doing. I dont find myself falling down to the ground a whole lot like when I was learning to walk all those years ago, so getting up off the ground isn;t something I train for lol.
You are obviously motivated to get yourself to the 300 mark. Should be easy for you to adjust to weighted exercise, and it takes less time too! Im in and out of the gym before some dudes get off the treadmill, and many never get the results they want and wonder why. Well, most are probably fucking up in the kitchen, not realizing thats where 80% of this battle is won.
And anything they do at a cross-fit, don't do, lol.