There seems to be a trend toward using hi hat cymbals that are larger than the traditional 14" size. I think part of the appeal is that larger cymbals have a lower pitch that blend better with the frequency range of the rest of the kit. Smaller hi hats tend to stick out more in the mix.
I've used the same 14" A Zildjian New Beat hi hats since about 1980, and I'm not exactly looking for anything new, but I thought I'd just experiment. I don't have larger hi hats, but I do have two 18" crash cymbals and more than two 20" rides.
The verdict? I probably wouldn't go bigger than 15 or 16" cymbals-and I just don't have two cymbals of either of those sizes to test. The 18 and 20" cymbals are a bit ridiculous as hi hats. But... I do kind of understand how this interesting, lower-pitched-than-usual sound might be fun to use, at least sometimes.
The hardest part of this test was adjusting to the feel of each set of cymbals as I moved from one set to the next. The larger ones don't respond as quickly as the smaller ones, so, just like when you try to play a figure on a larger drum, you have to work to articulate a bit more on the larger cymbals. (And you'll see that playing the triplet figure with each size was harder than I anticipated each time, so I never really played it cleanly.)
Equipment:
-18" Armand Zildjian medium thin crash
-18" A Zildjian medium thin crash
-20" K Zildjian ride
-20" K Zildjian heavy ride
-14" A Zildjian New Beat hi hats
-DW drums
-Blue Hummingbird overhead mics
-AKG D112 bass drum mic
-Apogee Element 88 A/D interface
-Logic Pro X
-Final Cut Pro
-iPhone 11 Pro