Believe it or not, The 84 is still fairly good all around. Nothing beats a dedicated hardware keypad (read: not a keyboard) for mathematics entry. I too delve into using the computer for mathematics. The calculator was way faster, entrywise. As for the 4-5 second delay in graphing, adjust xres, or get a faster calculator, or look into overclocking (not kidding). I also used an 89 for years, and 8 years later the 89 is still my go-to calculator.
To summarize : Computer for general homework == pain in the ass. Dedicated hardware is still the way to go.