I'v played in the NCL perm for about 15 years, its a decent standard. I was captain for ON first for 3 years, before moving to Brixworth this year.
If you play in NCL div 4, and don't score 1000s runs a season you will struggle in the perm, in honesty you need to be a real star in that standard to play (compete?!) in the prem. ON's 3rd team play in the 3/4th division, and none of those player would cut it in the prem.
How old are you, if your young and getting better than it might be easier to step up, too.
Rushden struggle to get a consistent team year from year, and like a few clubs at the bottom end they rely on OSP/Pro to keep them in the perm, they might well go down this year.
But like has been said already, they have a second team etc, so you can always play in that.
Come to Brixworth if your looking for a club, we're (No Swearing Please) Ace! ;-)