Can a 2cm lower ETT and 3cm lower stack make a big difference

I have recently been testing two mountain bikes: one with a 44cm (~17.5") frame, which I bought second-hand and one with a 45.7cm frame (~18"), which I bought new but want to return it as I like the second hand one better.

My question is: given the fact that the smaller one has 60cm stack, 40.5cm reach and 58cm effective top tube, while the larger has about 63cm stack, 41cm reach and about 60cm effective top tube, is it possibile I would not be able to tune the smaller one to fit similarly to the second one (e.g using a stem extender and/or angled stem to raise stack..)? Or should I be able to make them feel pretty much the same, in which case I can return the bigger one without regrets?

I like the equipment, looks and lower standover of the first one better, but I get some pain in my wrists, hopefully because of the placement/width of the handlebar and also some pretty annoyig middle-back pain.. However, the larger one does not really cause this pain, but I get more butt pain, ankle pain..

I also want to mention the smaller bike has 27.5" wheels, while the bigger has 29". I seem to like 27.5 better, though I only tested on road and a short gravel uphill road.

I am 180cm tall with a 78-79cm inseam.