Hi Shariff.
I don't think you should bother about the ph, especially if you are buying a new machine. This thing is build to last. I believe that when the time for ph replacement comes they will have paid off. One thing you should consider is that every time you put fresh ink in the machine it takes its date of expire plus the one of the ink you have in the system and calculates another one that differs from what you have on the ink label. My advice is not to overstock with ink because you might end up with ink containters which you can't use.
I am operating with both, Latex 800W and Colorado 1650, for a bit over 2 years and I am facing the machines' differences on a daily basis. I would describe the HP's build quality as mediocre. But it works...somehow. The 1650, on the other hand, might easily outlive this and probably the next two Latex generations
. From my experience so far there are two things where the 1650 fails compared to the Latex 800. 1. It can't print good black. By good black I mean dark, dense, pitch black. 2. The ink is supposed to withstand 80% strech but it can't. It cracks. However it is amazing how much it does sterch for a UV ink. So unless you print a lot of car wrap vinyls, as we do, you should not worry about No2.
Regarding the mismatch you talk about, you will not have that problem with the 1650. When we talk about large prints splitted in several places the size match is astonishing. Also not to forget - no color distortions thanks to the stable environment under the hood.
So, for wallprints, I think, the 1650 would be a very good choise.