Later I decided to lift the cpu to see the pins and check if there was some hackable stuff.
Sadly there're no possibilities, the 4th serdes interface (pcie,sata etc) is disabled and tied to ground, the SD interface pins aren't accessible...
I identified the rest of the boostrap pins, attaching the final modding pictures, if someone could add them to the wiki it would be nice.
The cpu speed seem to be hardcoded in some parts of the kernel, I still have some logs showing 800MHz:
[ 0.000000] time_init: processor frequency = 799.999992 MHz
Also
cat /proc/cpuinfo
processor : 0
cpu : e500v2
clock : 799.999992MHz
revision : 5.1 (pvr 8021 2151)
bogomips : 99.99
timebase : 49999999
platform : Freescale P1014
model : TP-Link TL-WDR4900 v1
Memory : 128 MB
But the performance gain is clearly obvious when hashing md5.
I set the memory to DDR-800, seems to be working nicely for now , another slight performance increase (5% faster md5sum, went from 16s to 15.2s).
It seems stable, I hashed 100GB of data several times with same results.