Hi, I recently downgraded from ICS back to GB on my ST25a. I was getting poor DL speeds via wifi but normal upload speeds. I am running stock sony rom ST25i_2.3.7_6.0.B.3.184_18.104.22.168+. The only one I could find was for a ST25i, but if you flash without baseband it's all good. I wanted root but found the only way for xperia u running GB was by flashing a pre rooted custom kernel. Which is ok but all of them messed up the wifi. After hours of scouring the net I found this http://forum.xda-developers.com/xper...b-ics-t2391208
It's basically a one click method and worked for me. I haven't tried it for ICS. Hope it helps someone.