I have not done tests which conclusively show measurable performance gaps.
That said, the gaps we're seeing at launch I know are the biggest, because the big players (COD, BF4, etc.) needed to finish their games before the platform had exploited the custom hardware benefits, so the perf gap you're seeing between COD and BF4 on the systems is likely largely because the custom hardware isn't being efficiently used, and when that's not used, the raw GPU advantage PS4 has over X1 isn't marginalized like it will be once the platform matures more... but I am *quite* sure (based on what I do know about both platforms) that our perf is close enough that resolution gaps will only get smaller (or disappear), and overall perf differences will require side-by-side comparisons to notice any meaningful differences, and that kind of a perf gap is inconsequential.
Ryse looks better than Killzone. Sure it's 900p and Killzone is 1080p, but it just looks better. I've played through all of Killzone, and Ryse has vastly (and noticeably) superior character models, not to mention the textures are more consistently high res, and the animation is easily better in RYSE... I anticipate that we'll see more of those kinds of situations... where the SPECS aren't want makes the difference, it's the devs/artists/content creators that will make the difference.
I get why people care about specs... but when they're this close, they really don't matter.
