Yeah I know MMX isn't emulated, I just used it as an example because most people know about MMX and also know it wasn't around in the age of the 8086 machines. It'd be sweet if stuff like that was emulated or patched right through to the MMX support on your physical CPU though!
Max, cycles are how games are timed in DOSBox. If a game can't run properly with max cycles, and there are a TON that don't like max cycles, then you have to specify an amount so it runs properly, but if the cycles vary from hardware to hardware, it makes things odd, but that's another discussion. It's almost as simple as you put it. If it's slow, give it more cycles, unless it slows down more in which case reduce them until max performance is found. If it's too fast, lower the cycles until it runs properly.
486 Launcher v2.0 is now under development!