On the matter of your PCB and the weight of heatpipe coolers.
The approximate weight of a 120 or 140mm fan is around ~7 oz. Excluding the fan or fans, much of the weight of the cooler itself is in the base or close to the base. Therefore -- less torque. The base itself exerts no torque. Add the fans, then there's some torque.
But it's really not that much. With the backplate and mounting hardware for most of these heatpipe towers, any stress is reasonably distributed on the board in that area. I just don't see any risk with them.
Then there's the possibility of pump failure. the pumps are getting better. But the system should shut down when temperatures reach a threshold level. Maybe there's even some risk that an aging AiO/CLC will leak -- I can't say.
But the risk as a matter of probability wouldn't amount to all that much. If it worries you, set your machine to hibernate when you're not right there using it and monitoring it. Or sleep-- then hibernate.
It really boils down to this.
If you look at the reviews of AiOs preceding the H240X, the edge over heatpipes can be closed with low-tech mods to the latter. So what temperatures are acceptable for a given overclock, in respect to a range of expected operating temperatures that Intel specs could suggest?
It's almost a toss-up between many AiOs and heatpipe coolers. And you can add the same low-tech mods to AiOs: WGusler recently started a thread about his project with a 4790K, Corsair C70 case and H80 cooler.
On the custom-water end, our resident guru confirms my own belief that folks tend to invest in excessive cooling with questionable benefit. If the overclocked processor operates in the expected STOCK temperature range for an AiO or heatpipes, it does little good to cool it so that the load temperatures are less than 5C or even 10C above ambient.
Under that latter scenario, you won't get higher clocks at lower voltage. You'll get approximately the same clocks at approximately the same voltage, or higher clocks with higher voltage. Mostly, you'll just get an overvolted processor with less thermal stress. But the difference in thermal stress between two different cooling solutions may not amount to a handful of beans. . . . Instead, you'd be facing the temptation to overvolt the processor with greater risk of accelerated electromigration. And excessive voltage poses more of a risk than any thermal stress, especially if the thermal stress is within the STOCK expectations of Intel.