If you are running win98 like you pretty much should with that combo, 256MB is more than you will ever need and more doesn’t change anything.
You might get few extra frames with faster CPU, but you would probably not notice until you’d install something like the fastest SlotA Thunderbirds available for the platform.
One option is to overclock your current CPU. If mobo supports increasing FSB, you could be able to increase it 10-15MHz. This would also improve the memory performance a bit as your PC133 sticks only run at 100MHz stock on that platform. Again, 10MHz would bring the CPU to 770MHz which certainly isn’t a major increase.
Or you could do what I did, build a goldfinger clone which lets you select CPU multiplier. I installed one to my 650MHz Pluto and it now runs at 800MHz on my EpoX 7KXA. To get more, I should mod cache multiplier as those just hit a wall and system posts, but won’t boot at 850MHz. GFD clone is a fun little project and return to the good old days of overclocking hacks.
TNT2/Pro/Ultra and V3 otherwise are quite on par and they generally trade blows depending on the game. TNT2 has better IQ, better textures and supports 32 bit colors, but V3 still performs better in some games.
All in all, your setup is very good for Slot A and Irongate systems and there is not that much which could drastically improve things, especially when Irongate is quite picky with graphics cards. If you want to tinker, by all means do so, but actual performance benefits won’t be that drastic due to the limitations of the platform.