i was also thinking of updating to the F.W i want and then trying untethered J.B and then an unlock from cydia but i have not been keeping track of the updates on that
First thing you should do is download tiny umbrella, connect your device and press save SHSH so that you can save SHSH for 4.1 and restore to that if you need to since 4.2.1 came out today and there is no usable jailbreak yet.