Don't listen to the compact guys, Go triple. You won't regret it. And seriously consider altering the gearing to 52 (or 53) -42-28. Use a 12 - whatever in back. I have been doing this for 40 (edit - I typed 49!) years and still love it. You get all the serious racing gears and shifts (and except for the low gear issues, a 42 middle is better/more useable than a 39) and you will have a much better selection of climbing gears.

Say you go 12-13-14-15-16-17-19-21-23-25. On the 28 you can use all but the 12 and 13. That 25 looks like the 30 of the compact, but look how much better next your choices are. You will find yourself shifting for little grade changes when the big plate guys are locked into their lows. And every time you do, there's that little acceleration you get that they will be struggling to match. If you are a climber, it's fun! And if you are not, having the right gear instead of just close can make a huge difference on a miles long climb.

At this point, you have spent nothing and you are looking at starting from scratch. Going triple won't cost you a lot more. Derailleurs? Basically the same price. Crankset? Maybe a few dollars more. BB? Same price. Chain? Same chain, you just remove fewer links. Shifters? Not very different.

I live in Portland, OR. There are serious hills around here. I have my 3 geared bikes set up as:

Good ti bike: 53-42-29 X 12-23, 25 or 28 9 speed (Campy - a sweet choice of cogs available)
Peter Mooney: 50-38-24 X 12-21 7 speed (SunTour Micro of the mid '90s with Command shifters; almost identical gearing)
Raleigh Carlton: 52-42-28 X 13-24 7 speed

On these bikes, the big ring is for fast company, downhill and overdrive. The middle is sweet on flat ground, small downhills and medium uphills. And the inner is the gear for serious climbs. Not just so I can survive them, but so I can thrive in them. (And yes, I know well about pushing taller gears on serious climbs. I rode last fall and '12 at Cycle Oregon with a 42-23 low gear on my fix gear. if you look at the course profiles, you will see those years were not flat. Completely different experience.)

A few years ago I set up a bike as a 53-39 with that Campy cassette, 12-25 or 28. Hated it. I was always riding a cassette without my favorite cogs and the 39 was not quite high enough to be a great flat ground gear and not serious when the climbing got really hard. The 28 tooth cog rarely goes on the bike with the triple. Exception: the Hood River Jackson Hill Foundation ride a couple of years ago. A century with dozens of climbs for 7000' as I recall. That day, the missing cogs forced me to often go one tooth larger than I wanted and save my legs a little. By the end of the day, I was glad I did! At mile 96 I had to do several one block climbs in the town of Hood River. That 28-28 low was none too! (And the compact guys? You know, it's funny, I don't remember seeing them in the late miles.)

Ben