i have a question about animated sprites

i want to create a animated sprite for a damage effect in my 1st person view
i used a solution 1280x1024 for my sprite, couz i want a good quality for this picture,but if i use this the frame rate will go down
if i use 800x600 it will be a little bit better
but if the solution of my sprite is lower, the quality of the sprite will be lower to
did someone know why the frame rate goes down?
did someone can help me pls?