It seems to me that the aggressive-specialist strategy is best suited to slower speeds. As malekithe says that has nothing to do with research speed since that all balances out between cottages and specialists and research times. Rather it is because slower speeds favour combat and that is an essential part of the strategy. You effectively get to fight more rounds of combat in any technological age and that favours the human player and an agressive one even more. But I think this strategy can still work at normal speed (at least my version of it).
In my mind specialists fit into the strategy as a desireable add-on that can use spare food instead of the "research engine" that some people think of. In a big empire that is rapidly expanding the important thing you need to do in a captured city is get some essential buildings in quickly to cut the costs and start producing something useful. Using slavery and working mines and other high production squares those buildings can be installed much quicker than if you try to work cottages and get commerce based benefits (beakers and gold) from the new conquest.
Also if I'm going for Domination I will soon have a lot more cities than the AI so it makes good sense to run Merchantilism to avoid giving away a lot in trade. Many of my cities will not have foreign trade routes and newly captured ones will not have the buildings giving the BS and BG bonusses from the trade anyway. Merchantalism also has the great advantage in a newly captured city of the free worker that can have many uses depending on the buildings captured or built.
I use food specialists as a means to control the population growth of the city as part of a happiness management technique. In the middle of a war a newly captured city will soon have war weariness (unless you have Mt Rushmore, a Jail and run Police State) and "we want to join motherland" unhappiness combined with 1 or 2 from slavery. You can soon have a problem even with a small or middle sized city with a good food surplus. How can we best use a high food surplus without working lesser tiles? Work mines, workshops etc for productivity or work food specialists to produce beakers and gold.
That is the underlying power basis of the aggressive-specialist strategy. The combination of high food, high productivity way of working cities with Merchantilism. My ideal civics would be
1) Representation for happiness in big cities and +3 beakers from my food specialists, settled specialists and the free ones from Merchantilism.
2) Bureaucracy (early) and Free Speech (late) since I will be working some towns and the +100% culture will help a lot of border and new cities.
3) Slavery - food is power and sacrifice is a way to control unhappiness
4) Merchantilism - Big empire doesn't help rivals trade and the free specialist is really useful in a new city.
5) Organised Religion - +25% help to build in those new cities and it helps Slavery work better too...
So a newly conquered city will need a Granary (to make Slavery work best), a theatre to boost culture (and allow an Artist if needed to further boost culture), a forge (to make Slavery and mines work better and gives access to an Engineer from Merchantilism), a courthouse, maybe temples (for more happiness / culture). Then we start building a productive infrastructure of BS and BG buildings which will depend on what tiles the city has to work. Libraries get built nearly everywhere (to give the Scientist option and they're cheap and they boost culture). Markets are good for more happiness... and so on. Alternatively I might build a Barracks or Drydock and build military but you get the idea...
I repeat the power of this strategy is having the combat bonusses from the aggressive traint, high food productive cities and running the civics I outlined above. That really means that you have to wait for the middle ages and renaissance before this becomes fully practical and you can go for total Domination. Of course you can have a limited early war in the classical / middle age to take over the cities of one AI opponent but that is just an expansion rather an attempt at Domination.
Another reason why any early attempt at Domination based on Representation only (as some advocate) is doomed is that you won't have important buildings in your core cities. You need to boost the BS and particulary BG in your top commerce / gold cities and for that you need to have researched up to Banking and built the buildings. I'm not entirley sure of this, but I feel an over expansion in the early game could delay the eventual and real non-stop run of Domination when it all comes together and all the civics and buildings are in place.
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