I have a cat here at home in Melbourne and it is closing in on 18 years old and had it ever since I was in primary school. It had 2 sets of kittens (5 kittens all up) that were given away as pets to friends and relatives, and then we desexed our cat to stop the production line

After the desexing is when my family bought a large farm in the Heathcote area so we bought 2 new kittens, raised them to full size in Melbourne, and then took them to the Heathcote farm to have as pest control.. when we took them away from Melbourne they were at the size of my permanent domestic cat.
One month after taking them up there, they had (unbelievably) grown much larger, thicker fur, more muscular, longer and bushier tails and gotten to sizes I didnt think domestic (feral for 4 or 5 weeks) cats could get to.
Then these 2 cats had 3 kittens.. they were born already massive as newborns, grew even larger than their parents at full size, with darker fur, and started to look like they belonged in the African jungles.
I was totally freaked out by the size and I would say that with the tail stretched out fully they would have been close to 1m long and weighed roughly 6 or 7, maybe 8kg's. I lured one in with food, lifted it very quickly (to avoid scratching) as it was eating, later lifted a 5kg weight, lifted a 10kg weight, and would say it was somewhere in between.
I know I know, it sounds a bit crazy that I lifted a feral cat but since we were heading over to the farm about once a month, they got used to people and knew that we provide food, so there was a good level of trust and I was recognised by them.
Eventually one kitten (male) was bitten by a snake and died. The parents and the 2 other kittens (one male & one female) vanished without a trace.
I dont know if they can grow even bigger than 80cm to 100cm long, or up to and over 10kg, but if they can then I wouldnt be suprised if its an Australian bred version of a feral cat that can get massive because of its system absorbing Australian food sources, climate, conditions, or whatever else could contribute to extra large size.