I have had a BGE XL since 2012. It is a great cooker, I have had very good, repeatable results. Having said that I'll also say I agree with what you said about your care and feeding the Kamado Joe. I use a Digiq Que DX2 so in addition to cleaning out the firebox, adding the lump charcoal, I also need to setup the Digiq blower. Not really a problem but certainly more time and effort compared to hitting the power button on my SM025. I got the SM025 for much the same reasons you are considering a CookShack box.
I still use the BGE but mainly for turkey and sometimes for chicken.
So what size? I purchased the SM025 because it has all the space I need. Simple enough. I considered a SM045 but, to date, that would have been overkill for me in terms of cooking space. I normally smoke enough for two to four people. When I do need more cooking space I have the BGE sitting right next to the SM025. With the two units you can cook a lot of food.
As far as taste goes - both produce a first class product. In my experience it can be difficult to tell the difference although I do find the cookshack can have a stronger smoke taste. That is mainly a factor of how much wood you put in the unit. One other 'thing' I like about the SM025 is it does a great job controlling/retaining a humid box. The BGE does as well although I usually (as in practically 99% of the time) use a water pan.
I have done 12 hour cooks in the BGE doing pork butt and Briskette. I have done the same with the SM025. One factor to consider it that with the SM025 I never had to think about checking on charcoal or being concerned if the unit was still running at 3 AM.
I am huge fan of both. For me the edge goes to cookshack by a good margin.
Yeah, quite a rambling post but perhaps it helps.