That would be about 1428MHz. Do remember that that's the limit and might cross 18W if used very intensively. I'd recommend 1224MHz CPU and 768MHz GPU because it's mostly fine like that. If you need more CPU, go up to 1428. If you need more GPU, go up to 921, but that's almost never worth it. So 1428/768 would be okay, I don't know if it makes a difference (only 0.5W in power draw) but the safer option would be 1326. It actually really is your choice. Higher clock speeds requires more Voltage, is more power draw and results in more heat which all decreases the life of the Switch. Overclocking always has risks. I just wouldn't go above the 18W, and always keep the temperature in mind.