CycloneIII Vs CycloneIV :: Urgent Help Required

Oh, by higher device grades, you mean speed grades. I was thinking you meant "higher architecture/process", i.e. Cyclone IV should be faster than Cyclone III. My mistake. Altera speed grades go in the opposite direction of Xilinx's, so slower is faster. So the high end Stratix V devices are -1,-2,-3,-4(and something will have to be figured for Generation 10, which will be even faster...). So the fact that a CIV -7 is slower than a CIII -6 is how it's supposed to work. (But again, it's not guaranteed across families).