Script timing is more important to put under the microscope than memory.
A region runs at 45 FPS, meaning 22.222222ms of timing per frame.
Open Stats by using ctrl-shift-1 and look at the "Time" sub-parameters at the bottom of the floater.
These show what's using timing in the region.
The more scripts in a region and the more things they do(see Script Events in the same floater) the more script timing will be consumed.
Back in 2011, reported script timing at the object level via llGetObjectDetails() and OBJECT_SCRIPT_TIME had more of a 1:1 reported vs. impact on script timing.
Ever since then over the years that ratio has lessened to an average of about 1:4, meaning an object with fully trended and constant script time of 0.125ms will consume 0.5ms from available timing in Stats.
This ratio also varies from what kind of script functions are in use especially if they trigger updates.
Once all available timing is consumed, region FPS will start to go down and timings will start to go up.
Script run rate % and eps will also go down since fewer script events will run per frame.
Also, understand that there is no fair resource distribution of script timing across parcels that each have different owners like there is with the distribution and limiting of prims per land owner.
So with all this general information, your basic goal is to not let all the scripts on your land consume more % of the region maximum available timing(22.222222ms) than the % of the land you own in the region.
You say you own 1/4 of a sim, so that would mean to not let the total script timing of your scripted objects exceed 5.555555ms.
Now, with that reported-to-impact ratio I mentioned, you have to reduce that value even further to 1.388888ms.
This does not take into account scripts worn by your guests which will also impact timings.
This does not take into account other activity that consumes timing, such as net timing (http usage, child agent connections), physics timing (physics movement, shape changes, pathfinding, etc), agent timing (object update checking in and around agent FOV).
This does not take into account if your region is a Homestead as multiple Homestead regions will run on a single host server CPU core and report lowered script run rates.
So "in theory" if there are only 4 parcels owners in the region, each owning 1/4 of the land, if each owner's scripted object totals don't exceed 1.388888ms, script run rates "should" always be near 100% and region FPS "should" always be near 45.
But, since we don't have fair script usage enforcement, it is all too common for one land owner's scripted objects to consume more than their fair share in the region.
Here are some examples of how people can abuse their share of script resources, whether knowing/caring or not:
One land owner owning a 4096 sqm parcel which is 6.25% of the land in the region, rezzes dozens of Amaretto horses that consume 33% - 50% of the script timing in the region.
One land owner owning a 4096 sqm parcel which is 6.25% of the land in the region, logs in dozens of AFK accounts whose attachments consume 33% - 50% of the script timing in the region.
Here is a feature request to bring us enforced fair script use.
There's also an issue that with today's high streaming cost content and the current generic land impact calc, that script counts/memory do not have any actual impact on land impact.
Here is a feature request to make scripts have a more correct effect on land impact.