Can I install a module of 2666mhz RAM with a 3200mhz RAM as a dual channel in on a motherboard that supports 3200mhz
Solution 1:
It should work, but both sticks will operate at 2666 MHz, not 3200 MHz.
Also, getting two sticks of different capacity (8+16 GB) will disable dual-channel, further degrading performance.
Whether you should is something you must decide yourself. Check benchmarks that reflect your typical usage.