Hi,
It seems, this is the main error.
[COLOR=#252C2F]140305 10:48:22 InnoDB: Completed initialization of buffer pool
[COLOR=#252C2F]InnoDB: Error: log file ./ib_logfile0 is of different size 0 50331648 bytes
[COLOR=#252C2F]InnoDB: than specified in the .cnf file 0 5242880 bytes!
If you have properly shutdown MySQL server before downgrade then all changes should have written into disk. In this case, Can you remove logfiles and try to restart MySQL again? MySQL will create new files when logfiles are not in datadir.