Recompiled with -O2 and the OpenWrt performance appears to have improved to ~ 26 Mbps.
--- a/dot.config
+++ b/dot.config
@@ -347,9 +347,10 @@ CONFIG_EXTERNAL_KERNEL_TREE=""
CONFIG_KERNEL_GIT_CLONE_URI=""
CONFIG_BUILD_LOG=y
# CONFIG_SRC_TREE_OVERRIDE is not set
-CONFIG_EXTRA_OPTIMIZATION="-fno-caller-saves -fno-plt"
-# CONFIG_TARGET_OPTIONS is not set
-CONFIG_TARGET_OPTIMIZATION="-Os -pipe"
+CONFIG_EXTRA_OPTIMIZATION="-fno-caller-saves -fno-plt -O2"
+CONFIG_TARGET_OPTIONS=y
+CONFIG_TARGET_OPTIMIZATION="-O2 -pipe"
+# CONFIG_SOFT_FLOAT is not set
# CONFIG_EXTERNAL_TOOLCHAIN is not set
CONFIG_NEED_TOOLCHAIN=y
# CONFIG_TOOLCHAINOPTS is not set