ferris is700z vs gravely zthd vs MZ61

I know these mowers aren't exactly in the same class, but I need help comparing just how much better the ride is for the Ferris is700z to see if its worth the money.

Ferris is700z 61 = ~6000
husqvarna MZ61= ~4750
gravely zthd =~5199 (or Ariens apex 60 for 5k...same mower)

I know I can get a suspension seat for the gravely or the husq for about 200. So that compared to the is700z suspension - is the difference dramatic or not? I don't think I can justify spending the money on the is2100 which i know would be nice.

I have 4 acres to cut - used to be hay field - so its not a subdivision lawn - not smooth. I'm using a 72" finish mower now @ about 4.5 mph. I need a ztr for various reasons.
I don't really NEED the larger hydros, commercial engine, ROPS on the Ferris - but of course those justify the price diff as well...I'm really only looking at it due to the suspension.

Anyone who has experience on the is700z vs a non-suspension mower of equal or lesser price - please let me know your opinion.

Thanks.

I just purchased my first zero turn mower.A Ferris IS700Z.Can't compare it to anything else but the property that I mower is very rough.The suspension does really work.I can visually watch the shocks working over the rough ground.Very pleased with the mowerso far.