First doublecheck your problem analysis. Is the problem loading the image, displaying the image or not related to the image at all. Use different test-sketches to pinpoint the exact problem. When I make a test sketch I can display 20 images of 10.000x664 pixels at a framerate of 60 fps. So no problem at all.

Test Sketch

1. PImage test;
2.  
3. void setup() {
4.   size(1200, 800);
5.   test = createImage(10000, 664, RGB);
6.   test.loadPixels();
7.   for (int i=0; i<test.pixels.length; i++) {
8.     test.pixels[i] = color(random(255), random(255), random(255));
9.   }
10.   test.updatePixels();
11. }
12.  
13. void draw() {
14.   background(0);
15.   for (int i=0; i<20; i++) {
16.     image(test, random(width), random(height));
17.   }
18.   frame.setTitle(int(frameRate) + " fps");
19. }

If the problem is somehow related to the image, then some suggestions are:

• Load the image in setup() once. This is not a suggestion, but a requirement!
• Use the OpenGL renderer.
• Divide the image into multiple smaller segments (you can do this in your program) and display the right ones.
• Use a GLSL shader.