Well I guess you must already know, everything on a GLCD including the text is stored as bitmaps. All that needs space to keep, read and transfer to the screen. I would not say which language is suitable; you must know the difference between a fast car and a regular one. Some professional compilers are fast cars. Once that is known, you can do wonders with whatever tool you have at hand. The thread on CLCD graphics by Art is just one example of what you can achieve.

I have worked on a monochrome GCLD with a 18F46K22 and done a bare bones text kind application using the Internal oscillator. Getting the speed to acceptable levels is the major aspect of the project. One tip would be to use byte aligned writes to the display. If your hardware is not finalized, ensure that you can read the GLCD besides write to it. Helps in doing pixel aligned instead of byte aligned displays.

Sorry if my words sound cryptic. That's what coding GLCDs does to you after a while