Here is a write I did on the RBR forum where a post frequently as well on the EPS system:
Campy EPS: I didn't really know what to expect with the groupset, and in fact before I purchased it I wasn't really sold on the idea of electronic systems. I have ridden Dura Ace/ Sram Red,and my Dogma last year had the Campy SR TI system. Ever since I switched over to Campy last year, I didn't think there was a better group set out there. I think many riders will have their opinions on the greatest groupo. Campy's cable system is super fast and allows you to shift through most/if not all the cogs with two clicks of the shifter. Before I received my new bike this year, I was already doubting the electrical system, I read some of early tests and thought it was going to be slower.
All I have to say is that I WAS WRONG (I know I am a Campy user so you may think my opinion is skewed)... The shifts are very fast, and extremely precise, and remember I am using a THM Clavicula Crank w/ Praxis Chain rings and a KCNC chain, so you would think there is a lot of variability with in terms of issues with the system. Early ride reports from cyclingnews.com, velonews and other journal sources indicated that there was a tendency at times where the rider can press the shift buttons with no response, and I do agree that can happen (very rare). I think the issue has to do with the rider getting used to the limited throw of the shift buttons when compared to the cable system. If you don't make proper contact at times you can see where the system might replicate this problem. Ride reports indicate that the there is a lag with the multishift. Yes I can confirm that, but it's not really noticeable. I think for that millisecond in lag, there is no way that any rider on any cable system can dump 11 gears that quickly. Remember, on the SR TI cable system, I think, takes 2 throws of the shifter to get all the way through the cassette, on the electrical system it only takes a press of the button. When is the multishit most noticeable, when you are pulling up to a stop light with less than a foot to stop and you forgot to get out of your hardest gear, just press the button and within your last pedal stroke you are at better gear when the light turns green. Of course there are other applications, but this one is one of my favorites . If you have the money to upgrade, I would say go for it, the weight penalty of the electrical system is nothing when you feel how quiet and smooth the shifting is.
Cons of the system:
The battery is heavy, and I am waiting for a third party to modify it. Sure everyone is going to make fun of me when they see my bike weighs 13.98 pounds, but remember, my prior dogma weighed the same and when you have a light weight bike you notice the little things. For example, I know/feel the weight at the center of the bike because the battery sits on the down tube, and no it doesn't affect the ride quality of the bike. One thing to think about with the Dogma (in my opinion) the bike feels a little heavier in the rear. I had a Madone 6.9 and one thing that was great about that bike was that it felt very light both front and rear. When you ride either versions of the Dogma they both seem to carry a little bit of the load in the rear. Why is this important? If you get a set of Zipp 404's/ 303s and are using the new EPS system then you are definitely going to feel the pull right off the gate. So when building your bike, with EPS or DI2 be mindful of the battery pack.
Campy.. once tuned the system is awesome, I haven't messed with the rider settings simply because the system works perfectly with my wheels, and most importantly my crank. I owe the guys at Winter Park Cycles for getting the system to work with the THM Crank, and I am not sure how they explained it to Campy since I wasn't using the OEM crank. If you get a THM crank (which I really recommend) just remind your dealer that there is a setting on the front der. to adjust the cage for wider crank sets.
Shifters: I think I'm still adjusting the rotation of my handle bars but I don't find the inner thumb trigger that reachable while in the Drops. This is where I think DI2 has a bigger advantage over Campy in terms of ergonomics. Shimano did well with allowing the rider to have the choice of Sprint shifters or shifters on the bar. After all, this is one of the biggest benefits of electrical systems, giving the rider more options to place the shifters where ever is more comfortable. On a side-note, does any know if you can adjust the position of the brake lever (i.e. bringing it inwards closer to the handle bar?).
DI2 Vs. Campy EPS: I have never ridden Shimano's version, but when it came out on the market everyone was raving about it. Which one is better??? EPS.. Why?? It's lighter, and most importantly MULTI SHIFT.. I cannot tell you how amazing it is until you ride it. I will say this, Shimano's next version of DI2 will probably kick some @SS, simply because it will have multishift, have numerous positions for riders to place shifters, and will be 11-speed. Campy will have to stay ahead, but in the electronic world after multi-shift there really isn't many other places to improve groupsets. I can see the loss of the electric cables, lighter weight and faster shifting as the next biggest improvements. I know both groups EPS and DI2 are an experience in themselves, Shimano will catch up to Campy but both electric gruppos are a huge improvement over cable.