In the US at least, we find speedtest on a iPhone using it's LTE connect, will most of the time beat the R11-LTE6 in a stock MT device just because of the aligned LTE band support with the carrier – why we've replaced a lot of modem in Mikrotiks.
If you use a M.2 adapter, which @SiB has promised pictures/writeup
, you have a lot of choices. So M.2 with Quectel approach may be better – I just never tried. We've used the Telit in a few dozen things, and work great. But the Quectel is likely to get better treatment in UI/support than other brands, since they plan on shipping a few different, newer Quectel modems for Chateau. So I'd be curious to see SiB's writeup, since a Quectel would better align with Mikrotik direction, I'd think. But the Telit do work just find and get you 5G bands, with no adapter.
The Telit's are pretty "Mikrotik friendly": selectable USB2 or 3 support (so no taping pins) and support ECM (so higher speeds work in V6), and most importantly come in miniPCIe. I'd skipped Quectel since they didn't have a miniPCIe in the 5G lineup. Downside for the TelIt is Mikrotik's UI doesn't show all the RF stats, so your likely need a few scripts with AT commands if you want get all the RF data, lock bands, swap carrier firmware. Depends on mode/model/ROS version, but sometimes you only get RSSI with the Telit (e.g. no RSRP/RSRQ/CQI) in UI.
Now the antennas for some of the 5G bands, different ball of wax.