i have both nexus 4 and 7. performance wise nexus 4 wins hand down. maybe cos nexus 7 has only 1gb ram.
the reason of why nexus 7 lags behind nexus 4 in performance has a few reasons:
1) The Tegra 3's memory controller is super slow (in fact, the one thing that's causing all those performance hiccups in newer games is due to this)
2) The Nexus 7's storage is using a way slower NAND flash...this is the reason why when you are installing something from play stores..performance seems to take a hit for a couple of seconds....it's because the Storage I/O couldn't keep up...
you can use the Androbench app to benchmark the Storage performance between Nexus 7 & 4 and you will find that it has one of the slowest (if not the slowest i've ever seen) NAND flash speed in terms of Random read/write...
hope that fixed this 2 things for the refresh..