AIOs:

• Last 6-7 years on average, up to 10-12 at most - but this is powered on 24/7
• Wear factors include fans, pump, evaporation of coolant
• If the computer is shut down/fans/aio off when not in use and not in a hot environment, you'll find they will last more than 8 years
• Pump life is usually 60,000-80,000 powered on hours (6.8 years to 9.1 years)
• Likely to get noisy (wooshing sounds) when the coolant evaporates to a certain point
• Tells you when it's time to change it
• Take up less room around the CPU which:
• Gives you room to work on parts like ram/ssds/graphics cards (without removing the aio)
• Keeps VRMs cooler
• Is easier to remove if required
• Require a case that supports it (most do)
• Have more parts that can fail(per the first point) so warranty/guarantee is important
• Most (good) brands have 5-6 year warranties (e.g. deepcool on some models, ek, arctic)
• Have greater thermal mass which means that it takes longer for them to heat up
• This means that high transient loads of \~10minutes won't thermally saturate the cooler
• Fans can run lower over the period to reach thermal saturation - therefore the fans can have a long "hysteresis" period where they react slowly to changes in temperature - which reduces noise
• Easy to clean
• Need to be mounted correctly (radiator and tubes must be above the pump)
• The best configurations mount the radiators in the top of the case
• If front mounted, the top of the radiator needs to be higher than the CPU block or pump
  • Tubes shouldn't be the highest point in the loop
• 120/240mm AIOs are not usually worth it
• They don't perform well enough to justify the extra complication
• Worth it only in SFF builds where they are the only option
• 280/360/420mm AIOs have greater surface area than air coolers and therefore can dissipate more heat than air coolers - but look at reviews to make sure that the exact model you're looking at is enough for what you're doing
• TLDR, get a 360/420mm AIO from a reputable brand for a high power processor

Heatsinks

• Last as long as their fans last, then the fans can be replaced
• Noctua fans last approximately 150,000 hours in general (17 years)
• Bequiet are nearly as good at 120,000 hours (13.5 years)
• Arctic fans are 80,000 hours unless you're talking their FDB fans
• Always provide cooling
• No pump/coolant to wear out means that there is "passive" cooling even if the fans die.
• Need to be mounted correctly
• Airflow should be front to back through a heatsink, not top->bottom or bottom to top in most cases.
• More difficult to clean as you need to take a heatsink off to clean dust off (usually)
• Less thermal mass (Noctua d15 will saturate in \~90 seconds) which means fans need to run faster for transient loads, so more noise
• Some are heavy
• Means that moving a computer around with a heatsink attached can damage the motherboard

For both AIOs and heatsinks, manufacturers often offer brackets to extend the life of the cooler.

The heatsink/AIO you choose shouldn't change significantly for the 7950x vs the 13700k, the 7950x puts out more heat than the 13700k when under load and at idle. This means is that it makes more sense to get an AIO (based on the above points) for a 7950x than a 13700k.

Do you need an AIO for a 13th gen? - no. Especially if you undervolt the processor.

Should you get an AIO to maximise performance on 13 gen - it depends on what you use the computer for.

• If it's for gaming, even the top end 13900ks doesn't need an AIO to perform well.
• If it's for compute (rendering/video/compiling/cinebench benchmarking or other intensive tasks) where you have prolonged heavy load - then yes, a 13700k or above should have an AIO attached to it. This is especially the case if lower render/compute time means more can be computed which means you get more money for the work.
• a $100 difference in cost is easily absorbed in 2 hours if you earn $50/hr and save 2 hours over a short period of time like a month. Note: arbitrary numbers used here.
• Personally I have a 13900k in my pc, not because I do a lot of compute, but because the time I save doing those odd compute tasks is often spent with family, which is very important (priceless) to me. I have a young child, I'll never get back time I don't spend with him now.

Consider also how much of the computer time is spent doing the compute task - eg if it's only 1-2% and less than 10 minutes a week, perhaps you can afford it to not be as fast for prolonged rendering, perhaps you can go grab a coffee while it's computing. Having a heatsink on it won't kill it, it will just run a little slower on those long tasks.

As a side note, if you get/have a 13th gen chip you should absolutely get and install a thermalright cpu bracket/contact frame. They are safe to install if you watch some videos on the installation & think about what you're doing, and will make a significant (10%) difference to whatever cooler you're using for very little money.

Ultimately, if you're running a high performance computer then an AIO makes sense, they're quieter, and you're likely to upgrade the computer (and cooling) before the AIO fails.