I recently tried exactly the same as my MR600 seems to require a reboot every couple of days. I went for the B818-263. I would not recommend ditching your 600 unless you are having problems with it.
Setup with the 818 was not straightforward (language setting aside).
The Huawei mobile app is buggy - It was reporting an error when I was creating the connection profile but when I later logged in to the device through the web GUI, it had indeed been working as there were numerous duplicate profiles. It took about 30 minutes of fiddling before the B818 would actually let me connect to the internet.
The B818 has an unusual external antenna connection so I could not use my poynting with SMA connectors, which is installed in the loft (not outside).
My speed dropped from a fairly consistent 40/20 with the MR600 (similar speeds on my mobile phone) to 15/20 with the B818.
I found the web gui to be relatively awful, although there's not much to be said for the Archer either in that regard.
I did not test WiFi performance as I use separate access points attached to my main router.
I shall be returning the B818.