The bass response of the Image X5s is definitely fuller, with more punch that the Ultimate Ears 700s, but that's not to say its better. While there's less drive to the UE 700s, they do sound just that bit more balanced and precise - no doubt thanks to each driver having to do less work than the one in the X5s. A pair of the Etymotic Research hf2 earphones, which both Riyad and I lauded for their clarity and accuracy couldn't best the 700s on that front either.
Take Hayley Williams' vocals on Paramore's acoustic cover of the Foo Fighters classic My Hero. While undeniably a great reproduction of a great rendition of a great song listened to with the hf2s or the Image X5s, through the Ultimate Ears 700s it shines brighter (sorry, no prizes for getting the reference).
It's hardly surprising that the dual-driver UE 700s can take single-driver earphones in a fight, but grabbing my trusty Shure SE420s highlighted the compromise Ultimate Ears has had to make in order to make the 700s so small. Every track that sounds excellent on the 700s has just a bit more sparkle with the SE420s.
Take AFI's Fainting Spells, for example. With the Shure's the opening acoustic guitar has a greater presence and when the track really kicks in (listen and you'll know what I mean) the UE 700s don't deliver the same power. Don't get me wrong, both are entirely listenable but the SE420s are still better. Just bear in mind that the difference is marginal and the UE 700's are a lot easier to live with, thanks to their smaller design.
It's a similar situation with Kilpsch's dual-driver Custom-3 earphones and I'd be hard pushed to say which sounded better. The Custom-3's are a little warmer and deliver more at the low end, but the 700s have more mid and top end clarity - personal preference is the key here, mine siding with Ultimate Ears in this case.
As an overall package, though, the contrast is greater. The Ultimate Ears 700 earphones are much smaller, arguably prettier (magpies would definitely approve) and by dint of being smaller and lighter they're more comfortable to wear for extended periods of time. Plus Shure's SE420s and Klipsch Custom 3s are more expensive, so if price is a constraint the Ultimate Ears 700s have a clear advantage there.
That the Ultimate Ears 700 earphones can be so small and yet sound so good is close to magic. That they're also priced lower than the competition is practically sorcery.