If you go with an Exo-Terra Desert Heat Wave you’d be looking at the 16W model which is 10.5” x 11”, which would cover 1/3 of the bottom of your tank as Matthew suggested.
I cannot speak to the intellitemp or zoomed, but having used the Big Apple Herp BAH-1000 before, I can say that it worked just fine but did require a bit of tweaking every now and then since it is an analog thermostat versus a more expensive digitally proportional one.
Regards,
Steve