cabert said:pyramids are still an option (not built yet AFAIK), but being financial makes the specialists a not so good option (well, an academy would still be good!)
About whipping, i don't share Eggolas' opinion : it's time to whip as many happiness buildings = temples as possible, wherever possible (the axeman "bug" can still be used, 25 hammers towards a temple is good)
I'm going to have to respectfully disagree. When I frequented the other civ forum, there was a lot of discussion about whipping after a slingshot. The general consensus was that the short-term advantage was not worth the decrease in population in the capital. You have a tremendous beaker advantage now over the other civs on your continent, one of which is financial and organized. This is the time to increase your relative research and production advantage, not squander it and let Washington catch up.
To me, the power of a financial civ increases exponentially with the advent of CS and Bureaucracy. But it requires that you rapidly increase the size of the capital to get the biggest relative advantage that you can. This is what makes the Liberalism slingshot a foregone conclusion. Otherwise, it becomes a race that could fall to America or someone on the other continent (not likely Monty or Isa).
A temple is nice, but seriously, it is not required for quite awhile. It's only a +1 happiness per temple. This early in the game, you'll get more from getting the wine, gems and furs into play (+3, +4 with forge), cottaging everything in London and making the other cities specialized, slave city-states providing London with happiness and health resources and the military units as well. Furthermore, Monarchy gives an immediate happiness boost of +1 for a unit and +1 for the wine (plus the additional commerce).
As for Monty, we simply have a disagreement as to tactics. I would prefer to block him off to the north by placing a city north of his capital, thereby leaving Tenochitlan open to invasion at any time (e.g., maces) without any buffer city to slog through. I would hone my CR skills on the barbarian city with the furs.
His Jaguar warriors will be useless against maces and he will build lots of them like the loony he is. Even if he goes for Longbows and gets them, CR2 maces are more than a match for Longbows.
In a nutshell, the achievement of the CS slingshot requires that you reevaluate all your options and the strategies you wanted to pursue for the ones that maximize the long-term benefits you'll reap from catapulting to a sizeable tech lead (pun intended). I have never lost a space race or Liberalism slingshot on Prince or Monarch difficulty after achieving the Oracle/CS slingshot. It simply puts a player in a powerful position to leverage the 50%/50% increase in the capital and the beaker lead of the CS, but only if one grows the capital quickly.
Your power rating is very low. You will probably have to buy some peaceful turns with Monty and pay him back later. If you switch to Monarchy and rework tiles, you should be able to get it in about 10 or less turns. With London having three units, that's 8 happiness cap. Taking the barbarian city right now (you have the axes), yields a quick one for the fur. Take your shock Axeman. He alone can do it. Moving the warrior south of London to London after HR is a cheap +1. Cottage the grassland hills. Cottage the plains. Cottage everything!

I'd run the new settler to the far NW to capture the fish/river position on the coast. [edit: nah, send it to the far east coast above Teno ... cut off Monty and his northward expansion leaving him to the jungle and his friends Isa and George. Let Monty develop the jungle, head for Machinery after Monarchy and take him down with Maces. You need lots more workers also. The CS slingshot leaves you militarily weak for awhile, but you'll get that back fast with Hereditary rule and larger cities. HR and Expansive work together well.
You can get to Machinery after HR fairly easily and in the 150AD period I suspect. Cottage like crazy in London. Move tiles around. Build a library there, not the monastery. Library is 25% to beakers, Monastery is 10% and you don't have open borders to spam religion yet (and don't need it). When HR comes, immediately build the winery.
Don't let Monty take a position above his capitol (broken record ... I know). Capture the eastern coast after taking the barbarian fur city. Better yet ... use the first settler on the east coast first and get another one chopped out for the west coast fish.
Tile micromanagement will shave a few turns off HR, MC and Machinery each bringing it to you well before 1AD. Build workers to spam cottages and build roads connecting cities and working the wine. It won't matter if George, Isa and Monty build towards you then. The maces will crush them, starting with Tenochitlan. I hope it's a nice city cause it's going to be yours!
Remember that forges work with gems to increase happiness.
Finally ... Caste System vs. whipping ... now is the time to decide. You'll get a quick border expansion to a city at the cost of some early turns of growth by utilizing an artist and the ability to use priests, merchants and scientists shouldn't be dismissed. Whipping on the other hand turns food into production. I would favor the caste system at this stage, but then I would probably head in a different strategic direction with a space race victory by the 1700s as the goal, while still taking as much of the continent as I could with my Macemen and Redcoats.