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I emulate GB/GBC/GBA/NDS on my phone so i can list exactly what the best emulators are to use, and the pros and cons of using them.
(Assuming this is an android)

For GB and GBC - MyOldBoy!
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I used to have a much worse setup than you and i found emulating anything from NES upto PS2 run at a minimum of 30fps (that was only on the PS2) so you should be okay. :) Hope i could help :D

It may be down to the Emulator your using. Try using 'No$GBA' which opens '.nds' and '.gba' game files. That's always worked fine for me :) Hope i could help.
Link to NO$GBA :...

I'd Recommend Using MyBoy! on Android or for PC my personal reccomendation has to be VisualBoyAdvance. But i wouldn't use save states too much.