Unfortunately that's not correct. If you search this thread for posts by "joevt" you will find a number of detailed technical posts regarding this issue. The bottom line is that we cannot trust the resolution information provided by macOS in
some places. For a true 5K monitor (5120 x 2880) driven by a
single DP-In, the actual frame buffer resolution is
4096 x 2304 (9.4M pixels). This is more than 1 million more pixels than a 4K monitor, but still a little less than true 5K.
The 34" LG monitor that you are considering (5120 x 2160) is
11M pixels, which is more than the
9.4M pixels that a full 5K monitor receives from this motherboard. That is why I don't think this system will provide full 5120 x 2160 resolution through the Thunderbolt port.
However, if you buy a Gigabyte
GC-Alpine Ridgle (
not GC-Titan Ridge) then you will be able to drive this monitor at its full resolution via Thunderbolt 3. The nice thing about the GC-Alpine Ridge is that:
- Even though it needs a Thunderbolt Header connection to the motherboard (THB_C) -- and the Designare Z390 does NOT have this header -- we don't have to worry about it!
- Just connect 2 DisplayPort cables from the AMD Graphics Card to the 2 DP-In ports and you should be good to go.
- However, we should not expect any other Thunderbolt devices to work because the THB_C header is missing. Only Thunderbolt 3 monitors can be expected to work.
The reason to stay away from the newer GC-Titan Ridge is because:
- The Titan Ridge controller on the card is the same as the Titan Ridge controller on the motherboard.
- The motherboard will disable the built-in Titan Ridge controller because it sees a duplicate device. The Gigabyte firmware should be smart enough to support both controllers, but I don't think it does.
- So the on-board Thunderbolt ports may not work.