You can think about going up .25” in diameter when you start to consistently pack, or totally fill up the tube girthwise, which may or may not include head packing. If you just start touching the sides of the tube or your base area packs, but not midshaft, this is still not fully packed. When you are fully packed, you will know it, cuz your entire shaft will look kind of squished on the walls of the cylinder.
Even when fully packed, yes, you can still use the same tube to go for length, but you have to be careful to reduce pressure after becoming packed. If you don’t, there is a tendency to get water blisters forming on the head, because all of the pressure is now concentrated there and water blisters on the head are a bitch and will stop you dead in your tracks as far as pumping goes.