You could expect
very minimal gains in most titles. Going to 32gb would make 0 difference in almost all titles. RAM frequency could make a bit of difference, but not usually bags of it.
If you had no RAM at all (i.e. you were building the PC from scratch) I'd advise you to get 3200MHz/3600MHz over 2400MHz because the price difference is small and there can be some gains. However, since you already have the RAM, my suggestion would be to stick with what you already have. Because whatever improvement you get it's not going to be £150/$/€/whatever worth of 'better'.
More than 16gb RAM could benefit video editing, although tbh given the rest of your setup (that i5) it would seem a waste of cash to buy it.
I don't mean the following in a negative way, but rather as a pointer for future upgrades.
The i5 7640x is an appalling invention by Intel. The problem with it is that it is a quad core i5 CPU (4 cores, 4 threads) on the X299 platform - i.e. it is a mid-budget CPU - on an extremely expensive, workstation-focused platform. The more popular choice at the time would have been to buy an i7 7700k CPU (4 cores and 8 threads) on the Z270 platform, for probably about the same total price and giving better performance for just about everything. There is virutally nobody that the 7640x would have made the most sense for at the time of purchase. It's shameful Intel even released that part.
When you come to upgrade, for instance if and when you find the 4 cores/4 threads of that CPU to be holding you back, make sure to look at the consumer level platforms first, not the HEDT ("high end desktop" which really means professional workstation) first. The Intel consumer platform (currently Z490 etc motherboards) supports CPUs with upto 10 cores and 20 threads, while AMD (B450/B550/X570 etc mobos) support upto 16 cores and 32 threads.
You've already sunk money into your current platform - my advice would be to keep using it for as long as humanly possible to get as much out of that money as possible. If you could stick it out to 2022 for instance we might be on new technologies like DDR5 RAM by then. And when you do upgrade your platform, beware of the platform and CPU you buy