When running option 21: should we pick Nullify or Un-nullify?
Also, is this needed if we flash the OOM script Srkineo provided in the downloads section?
It used to be that you could do everything with the supercharger script and you didn't need that OOM-priority zip. But in ICS things are more difficult. If you just flash the patch in the OP you should reach 50% supercharged. This adjusts the out of memory groupings and makes the launcher very stable in memory (so no launcher redraws). You get another 50% by adjusting the minfree values. The two pieces together tries to make sure that you always have some free memory and that the you clean out "inactive" processes more intelligently. The more aggressive you are in the minfree settinds (super is most aggressive) the fewer lags you should see in a single program (playing a game for example) but you may have issues keeping a lot of apps open at the same time.
For the nitro lag nullifier (#21) you want to nullify (N).
Even if after all this you still have lags, you can set up the engine flush script to run every few hours using a task scheduler like cron or tasker. This script is part of the supercharger script and it will try and free up as much memory as possible, including clearing out the cache.