Temperature control feedback

I am curious about size of heater and effect on how quickly temperature increases with heater on and decreases when it is off.

In summary, 125 G DT with about 35 G sump. 2- 500 Watt heaters in return section of sump. 2 separate Apex monitored temp probes in other ("upstream") portion of sump.

Heater set to turn on (one set to be back up) at 77.5 and off at 78.5. A complete cycle, from 77.5 to 78.5 and back down to 77.5 takes about 5 hours and that is pretty reliable looking back at Apex graph. Increase and decrease generally appear to be about the same rate.

So I have some questions:

Is that about right as far as not fluctuating too much?
Would smaller heaters cause less rapid up and down- meaning if they are needing to be on longer to reach the off temp would the rise be slower?
Is my this cycle considered stable enough?
Should my range be tighter to keep more steady but require the heater to cycle on/off more often?

I did notice that when heater is on, the return compartment is noticeably warmer than rest of system. I have a tunze ATO with sensor in return section, so not real worried about heated section drying up but I guess it's not impossible.

Thanks for any ideas or suggestions.