Well it is hard to say due to the fact that some may never gain two inches, others may gain that much and in some cases even more. You will have to read your signs that your penis gives you. I would suggest that you keep a good eye on your progress and if the gains stop or slow down you would then think about switching it up.
Is there a specific reason you would only want to do those specific angles?
Simply put, I havent managed to make a rig to do SU or OTS very well. Swinging the rope over my chair causes the rope to slip, even with something "holding" it. And I cant put a hook in my ceiling since Im renting my place.
The highest angle I can comfortably do is about 45 degrees upward, trying to go higher becomes a rather clunky hassle.
I was considering getting some 2x4s an hinges, to build a collapsible elevated pulley mounting thing. Need it to be storeable because I dont have much room in my place, nor do I want people asking me "what the heck is that thing?" when they come over.
I sit at a computer when I pe so when I get to that poit of going straight up or at an upward angle I will probably attach a pully under the desk and rig it that way. I will run a cable with quick release hooks on each end, clip one to the hanger run it through the pully and then clip it to the wieght.
If you are sitting in a chair that has arms why not hang it over the left arm for a set then over the right arm for a set. many options to go with.