A new way to add to the previous guides
Again SPQR mission, and by all mean do the combos on the first section you'll net around a 30-40x on the first room, then 60x on the next room this is a big room with lots of enemies...BUT, later on after you climb the building..
get to the colosseum where there are pila archers on the roofs, kill them, jump down
now you should have max focus by this point if you break the pots along the way
So, use the focus, kill the first three, then focus, next three and focus next three
this normally gets around 60x and with untouchable bonus, focus bonus +xp
-- I got about 50'000xp from this checkpoint