Stiffer springs than stock = better???

i was thinking about getting stiffer springs, since my jimny tends to sway a lot during turns and i'd also like to make it a little more suitable for small jumps and better to take turns on tarmac, any advice?

also, talking about springs, i'd like to change valve springs, would stiffer ones be more suitable for high RPM use? not too stiff, just stiff enough to be able to withstand 7000 RPM without an issue, obviously i'll slowly upgrade the rest of the internals to be able to use those RPMs before actually doing it.
what are some good makes?
also, do you guys know about the max safe RPMs the non-VVT M13A can be pushed to? i say safe as in "not that noticeable" engine life span reduction or increase in problems. I sometimes rev it to the hard redline but normally change at 6000 if i'm training on dirt or doing pulls to hear the engine roar

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i was thinking about getting stiffer springs, since my jimny tends to sway a lot during turns and i'd also like to make it a little more suitable for small jumps and better to take turns on tarmac, any advice?

You need to take a holistic approach to handling, springs are only one part of the "package", tell us about the vehicle, and what has been done to it, is it stock or has it been lifted/lowered? are you running OEM sized tires?  what condition is the suspension in?  how many miles on the shocks?

An important consideration is how the vehicle is going to be used - setting it up for tarmac use is decidedly different to setting it up for "off road" usage.

It's important to bear in mind that a Jimny will not, and was never intended to, handle like a sports car, it's a tall, narrow, top heavy, body on frame, 4WD sitting on live axles.

Stiffer springs will reduce body roll in a turn, but at the expense of ride comfort - replacing worn shocks and stabilizer bar hardware can significantly reduce body roll without negatively impacting ride quality.  Taller tires also impact vehicle sway, switching to a lower profile tire will reduce sidewall squirm

yeah, you're right, i didn't include what has been done to the car, even though it's not much.
i replaced the dampers with monotube reinforced ones, made by a company that specializes in offroad use, they're almost new, they have less than 3000 kms but they've been used roughly, i go fast offroad, on gravel and dirt and do little jumps and hit holes pretty hard, even though i try to shift the weight of the car to soften the blow. i want to put stiffer springs to avoid bottoming out the suspension because of the holes and for the body roll.
the car has stock 15" rims and 205 all terrain toyo tyres which i keep inflated at the pressure specified in the manual, or just a little less to improve grip a little bit (obviously at the expense of response), it isn't lifted nor lowered and generally has mild mods.
i don't care about ride comfort as much as making it a little more stable.

also what about the valve springs? any advice in that regard?
 

And are these "monotube reinforced" shocks correctly valved for the Jimny?

Yes they should be valved correctly, they were made for my model and by a trusted company where I live.
To be fair, I don't have a lot of experience working on cars, so I follow the advice my mechanic gives me, he races in his youth and won some minor championships here in Italy, and loves my Jimny so he offered to help me when he can.