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As you were saying, Micro SD card 8 GB, 16 GB, 32 GB, 64 GB and 128 GB sizes are supported. However, some products may have been tested by Intel or a third party. When tested, they showed no major impact on performance, functionality, or compatibility. Having said that, it is important to mention that you can purchase the products in question at your own risk.
Hopefully, other users will share their feedback with these Micro SD cards.
Intel Customer Support Technician
Under Contract to Intel Corporation
Although the Wiki says SDXC support up to 2 TB those cards do not exist ...... yet.
Source: Secure Digital - Wikipedia
I can confirm that Sandisk Ultra 400 GB is working on my ComputeStick - STK2mv64CC (So my best guess is it should also work on the stk2m3w64cc).
I've recently replaced it for the 200 GB from the same series / product line.