I prefer pairing West Point with the Heroic Epic. That way you avoid the diminishing returns on production, maximize your number of highly promoted units out of the box and can use the IW city for wonder building without wasting HE during those turns.
On the diminishing returns angle, consider that your HE and IW cities should each have 60+ base hammers and forges by the time you can build IW. HE only helps when building units. When IW can be built, you're building riflemen, cavalry, cannon and maybe infantry, all in the 150-210 hammer range. Let's just use a hypothetical 70 base hammer city with a forge. HE makes that 157 hpt when building units. That's 1-2 turns for every unit, even before considering overflow. In fact, that city will be able to produce every modern unit in 1-2 turns, as well, especially considering the 53 hpt boost it will get from a factory and power (grand total of 210 hpt). Add IW to that city and you get 227 hpt, good for a unit every turn. You've saved a turn off every unit that was going to cost 2 turns, which is going to be far less less than every unit you're building. In my games, I'm able to keep the overflow going so that pretty much all my HE city units after a certain point are produced in a single turn.
Now, consider a second city with 70 base hammers and a forge (which shouldn't be difficult to imagine). Without HE or IW, it's producing 87 hpt, good for 2-3 turn units. Add IW to it and you've given yourself a second unit producer as good as your HE city, meaning that you've got two cities producing a unit every 1-2 turns. You've shaved a turn off just about every unit you produce. Remember, it's all about turns, not hammers. The hammers are just a means to minimize the turns.
Two cities producing roughly a unit every turn or so also lets you diversify and specialize your unit production. One of my favorite things to do is build a stack of Combat IV marines in my HE/WP city (easy with Charismatic, but a GG-eater without), then send them overseas to attack coastal cities for the sole purpose of gaining Combat V and Commando promotions (then starting down the Drill line if I gain enough XP). With this approach, I can do that while still pumping out CG infantry, CR tanks and whatever else I need from my IW city. My other cities supplement the army with regular line troops, but these two cities form the backbone. With HE and IW in the same city, you're having to rely on your next best production city, which is going to be far behind your HE/IW city, to provide your elite troops through WP.
