NoMachine fully supports multi-monitors or large screen up to 4k resolution. In case of multi-monitors, the global resolution is given by the sum of resolution of each monitor. For example, if you have four monitors at 4K, the final resolution is 4x4=16 k. While it's possible to display a NoMachine remote desktop on one single monitor at 4k, it's not possible to do that on a 4-screen full/Ultra HD multi-monitor setup. Tests in our labs evidenced that the NoMachine session can be displayed up to a 2x4K resolution (H.264 generally allows up to 4K, while VP8 supports a maximum resolution of 16384x16384).
The implementation of this feature request: https://www.nomachine.com/FR05N03113, which permits to treat each monitor of a multi-monitor set-up as an invidual monitor, will also permit to noticeably increase the upper limit of maximum resolution supported.
Besides the encoding, another possible problem can be the maximum memory size that a 32bit process can allocate on Windows. This limitation can be overriden only by NoMachine packages built for Windows 64bit architecture. See https://www.nomachine.com/FR09Q03870.