With the progression pace of MAME, all the builds available, varied PC capabilities (even between same-clocked but different brands), this excercise is fruitless and never-ending. Go back 10 years on this scene and many were asking the same questions, which soon becomes irrelevant as you will find out - it's the playability factor rather than the clocked speed that makes the difference, which depends greatly on emulator maturity. Think back to when .chd's were first introduced around 0.7x and KI ran like ---steaming pile of meadow muffin--- - even now running older builds on new hardware shows higher PC demands for that game, whilst a later MAME build on a lower-spec PC will produce equal results.
It's swings and roundabouts, so just enjoy what you can. There isn't much left needs properly emulating that anyone is really currently missing, and moving into 6th-generation console emulation the games aren't particularly suited to arcade controls or cabinets anyway.