hicky, if you have saved SHSH and AP tickets for 4.1 you should be fine as apple is still signing for 4.1 but not 4.3 !! (assumeing that you have unlockable baseband) Or you can stay there at 5.1 with tethered jailbreak !! If i were you i would not worry about downgrading and jailbreak and unlock at 5.1 (remember nerver update iphone if you require JB and UL)