Okay, so I forgot combo. Although they are also usually divided into speed (CadBloom, Bargain) and control types (Stasis, Prison).
Secret Force - Secret Force is hard to define, decks with strong search engines can be modal as you say, although most choose to find one strategy and stick to it (as Living Death did). Hmm.. a third turn Force is certainly a clock, but I think that the spirit of the deck is more control-based (Feeders and Weavers, wasn`t it?) and the Force was often about the card advantage generated by the Verdant than it was about the 7/7 guy himself laying the smackdown. The game rarely ended before turn 5 therefore you gave your opponent plenty of time to use his strategy and I think that makes it Control. It can move fast, but a second turn Skittering Skirge could be a fast kill (turn six with Corrupt backing) but that doesn`t make Black control a beatdown deck - it just makes it a control deck that attacks early.
Classic Sligh - Control. A very beautiful deck, but certainly control every time.
Necro-Drain - Control. 1-1 swaps combined with huge draw effects.
Hard and Fast rule: Unless you are laying down a reliable 5-turn clock then your deck is control.