Hi,
what type of language you will use, asm or C. If will use a C i think that KEIL is the best, but you can use a GCC too. If you can use the Cygnal 8051 controller will have compiler, 25-100 MIPS, flash, and many more futures. I several time in last 4 year looked this controller, but every time the project time was to short and i dont use it. Yesterday i receive the evaluation board and test it, controller is very, very good, and SiliconLab IDE is very nice, i can suggest this x51 microcontroller.
About the project, i has one very similar, if understand right what you must design. If you have a some specific question i try answer you.