Check these benchmarks done by anandtech on Nexus 4 and 10 AnandTech - Google Nexus 4 and Nexus 10 Performance Preview
yes read it, as anand sir says its Android Optimization issue.
In GL benchmarks, Adreno 320 beats all other android phones. next year we would probably see Galaxy S4 with Mali T-604 retaking the crown.
have a look at Optimus G.
AnandTech - LG Optimus G Performance Preview
it blows every other smartphone out of the water as far as Linpack is concerned. but sucks badly in browser, javascript benchmarks.
But then they have sorted it out and final version will be much better. it topped the sunspider (exclude the lava phone)
AnandTech - LG Optimus G - JavaScript Performance Improving in Final Software
so as guru_urug said Google hopefully would resolve it in final shipping version. if you see Galaxy S3 with Exynos 4, which has lower CPU/GPU performance has done very well in browser benchmarks, their optimization is pretty good. Galaxy S3, Nexus, S2 seems to have excellent browser benchmarks may be coz Exynos chipset is Samsungs own. ofcourse somehow they didnt repeat with Exynos 5, Nexus 10.