1-
One of my classmates that is a good welder tried the 3G and 4G position because he could not do the 2G!
What how bout that?
This made me laugh

:):) Dont go ahead to the 3g/4g if you havnt got the 2g down!
2-If their x-rayin you guys for your certs thats rough man

Most certs you only gotta pass a bend test. If your welds are gettin x-rayed my advice would be to get that 1g down dead nuts perfect, passin x-ray before you move on to your next position. Practicing your other positions wont -hurt- really, but for me its easier to concentrate on one thing at a time, rather than tryin to get 4 things half way done then goin back and doin em again. Catch my drift?
3-Heres the thing about certs, and "legitamate" welders-Certs only last for 6 months. So if your not using that cert i.e. have your employer signing off on your hours, you lose the cert if you dont get a job
using that procedure than your out your time and money you spent to get that cert. All that being said, most(well, in my trade, almost all) employers have some sort of gate test, which is specific to whatever your going to be welding on.
What I'm tryin to say is your not going to see very many adds in the paper for a welder with this cert or that cert. Usually what youll see is "welder capable of passing a 3/8 inch 4g plate test with stick/tig/mig" or something similar.