Last year I bought a new bike that came with 700x38C tires and full length fenders. It had a coaster brake on the rear wheel and a very inexpensive single pivot sidepull caliper brake on the front wheel.

Over the course of the year I went from being a marginal cyclist to being a more committed and aggressive rider, and I made hardware changes to reflect that. I swapped North Road bars to drop bars, a twist shifter to bar end shifter, and fat tires to thinner rimmed wheels with narrow slicks. I took off the fenders because they rattled in the wind. My speed has drastically increased, but my braking power has not.

I installed a Tektro R556 dual pivot caliper brake on the rear brake bridge and it just barely fit properly with the pads set at the full 73mm reach. I'd like to have a more powerful front brake as well, and it seems more efficient to have a bigger wheel and normal sized brake. There is so much extra room with 700x28 and 700x32 tires mounted that I think I could actually switch to the bigger 27 inch wheels and use a normal short reach caliper instead of the long reach. I think the new style road calipers are marked around 39-49mm. Is the move from 700 to 27" wheels comparable to the difference in caliper reach from long reach to the normal range? I know most people go in the opposite direction and tire choice is more limited, but the overall proportions would seem more balanced. I wouldn't mind lowering the seat post accordingly. Anyway, is there a reason I can't get a bigger wheel and a shorter reach brake?

You won't be able to utilize a shorter reach brake. The difference between 700c and 27" is 8mm in diameter, so the brake pads will move up 4mm when you do the switch. Keep in mind that your tire choices will be much more limited with 27" wheels and that you'll have less room for tire/fender clearance.

700c: 622mm diameter
27": 630mm diameter

Huh? Move the seatpost? That has everything to do with the distance from the pedals to the saddle, and absolutely nothing to do with what tire size you're using.

I was thinking that bigger tires would move me farther off the ground, so adjusting the seat would maintain the same standover height...but you're right. 4mm doesn't make enough difference to be worth that idea. Thanks for the tip anyway.

I was going to say that in my post but I forgot. You really don't have anything to gain by switching. Better to stick with the 700's for the tire choices.

Also, standover is irrelevant. The saddle needs to be set according to where your feet fall in relation to the pedals.

For 4 mm of reduced brake reach you're limiting your choices in rim and tire selection, but if you insist, I suggest the Sun-Ringle M13II, available in 27x1 with 32 or 36 holes. I've been happy with the 700c version for a couple years now.

If this '700C' bike can't use a proper brake with 700C rims, I'd swap out the fork.