The monochrome will always give a better resolution but like I said above, I think the gap is closing. So, to me, the gap in resolution between the two is not that dramatic but probably an AP expert would argue otherwise given the very nature of having to use 4 pixels to give you the color vs. a 1:1 with a mono camera and color filter. Between my so-so eyesight, Bortle 6 skies, and my PixInsight processing skill level, I find little difference. That is why I have not focused on mono using LRGB filters but I really like the mono for narrowband imaging. People can disagree but it isn't a wrong or right thing, it is merely personal preference as there are so many variables (e.g., your sky conditions, time you have to image, cost to buy various accessories, processing skills, and simply how far you want to go to get an image that is pleasing to you).
Yes, you certainly can do a ROI with the 2600 to mimic the 533. First, the 533 came out months before the 2600 and I bought it when it first became available. I really like it despite the smaller sensor. It is at a great price, low dark current, no amp glow and very easy to calibrate (vs. the 294 which I had). Then, the 2600 came out and I was intrigued by the larger sensor (largest I have had) in addition to the same newer technology as the 533. However, it really needs a lot of computer power to process the larger 16-bit image files vs. the 533 smaller 14 bit files. Second, I have a C11" EdgeHD in a permanent observatory with an 80mm APO triple piggy backed onto it. This gives me unlimited options in a FOV between the 2 scopes, using reducers or not, and the two different sensor sizes and having them both on a scope limits my need to go climbing up to change a camera. I may eventually sell the 533 after I feel 100% comfortable with the 2600.