It really has more to do with which Level IV league you promote into. I have seen some Level IV leagues where even the best team doesnt look that much different than the solid Level V teams...however, I was promoted into a brutal Level IV league, and its a completely different ball game. My league could give some Level III leagues a run for their money. I played a guy yesterday in which 2 of his players have a higher salary than my entire roster. The average payroll in my league is over 150K, and there are two teams with 200K)+ payroll in my league.
There are two 53K+ centers in my league, a 48K PG. Again, I have seen some Level IV leagues where the highest salary player is less than 15K.
That said, as brutal as it is, whoever survives this league will be much better equipped to compete in level III.
Good luck!!