If you want to change engine this way, may as well get a wira cheap cheap and modify.

You no need be scared the warranty will be cancelled if change engine or gearbox, I reassure you most of the car major warranties will be gone. So no need worry since you get a definite answer now.

Hit an LCP (lighten crank pulley), be it the budget Works Engineering or the premium Mytheo. Plug and play item, if needed just ask mechanic to switch it out if claiming major engine warranty. My small SC did not even bother to see if its a mod, just claim only.

LCP will shorten the gear ratio means it will switch the gear pretty fast and increase acceleration without car original gear ratio pulling the car back (PE got major tendency to do that). Thus without LCP, I won't even consider driving PE now.

As for makan manyak petrol, 2 major points,

1. Your right leg. If you're one that like to tekan minyak, better go buy a viva to save FC, coz any car pun makan minyak if you don't change your driving style.

2. PE is a heavy car with an engine that has a weak lower torque. You got to live with it's makan minyak tendancies unless you go for lots of mid speed highway run. Either that or go change car to viva. You should have gotten a Myvi in that case.

persona is not fine bcoz you previously drive a putra with gsr engine.
the power to weight ratio is much difference therefore ur putra give better fc.
another thing is the characteristics of campro. it is a high rev engine where the torque came late which means you need to rev high and as usual, higher rev, higher fuel consumption. if you ask me, with your current problem, yes, you will get better fc if you change ur engine and gearbox.  but remember the car will not be as good as your putra because of the weight. if persona are made at nearly just 1000kg like those vios, city, almera, basically you will get fc as good as them too. however it is not really worth it if you just bought the car then throw in another 10k for the conversion. basically, the warranty that you really need to concern mostly are just the engine as gearbox where when they void ur warranty this two are very costly to repair which everyone are scared of. so if you actually plan to change the engine and gearbox, warranty is not a problem anymore. you might not even have to go back to proton anymore. just make sure you have a reliable workshop for routine maintenance that can make sure everything is working fine.