I have to look up the official specs of 1st generation i7 860/920 all the way to i7 4790K to confirm but I am pretty sure some later processors aren't recommended to be operating with 1.65V DDR3. Also, there have been testing done on latter Intel CPU generations where the CPU would operate at slightly higher temperatures when paired with DDR3 1.65V vs. DDR3 at 1.35-1.5V. what this means, if someone bought 1.25-1.35V DDR3/L, it's technically possible to reuse it in SB->Skylake platforms without any issues. Samsung's 30nm 1.35V DDR3 1600 that overclocked to 2400mhz was a very versatile kit and would be great to use in a Skylake DDR3L motherboard. Also, generally speaking RAM that starts off with lower voltage tends to have more room to overclock than comparable RAM with higher voltage. This isn't always true but as far back as DDR1, generally speaking the best binned RAM sticks have the lowest voltage balance against the highest speed from the factory. Even in my own experience it's often way easier to overclock low voltage memory with tighter timings to higher speeds and looser timings but it's much harder to go backwards to get tighter timings on high-clock speed sticks. Your experience may differ.
There have been plenty of examples of this in the past.
Since my experience from DDR1->DDR3 completely aligns with these results with various RAM from Kingmax, Kingston, Corsair, G.Skill, Geil, I will generally choose memory with lower voltage and tighter timings, even if it's slightly slower (i.e., DDR4 2800 1.2V vs. DDR4 3000 1.35V).
A real world example today would be this DDR4 2800 1.25V Trident memory. This memory is likely to have massive overclocking headroom because at 1.35V and looser timings, there is a high likelihood that on a solid motherboard it could be configured to operate at DDR4 3866.
This is how some Kingston Hyper X DDR4 2133 kits can easily operate at 3000-3200 mhz speeds with a bump in voltage and looser timings because they come with awesome Hynix memory that has low voltage.
While it always pays to read reviews and see what exact chips are used and how well the kit overclocks, your assertion that buying say DDR4 2800 1.35V DDR4 over DDR4 2800 1.25V basically makes no difference is not going to hold water for anyone who overclocks. In recent years almost all PC builders stopped focusing on this point because overclocking DDR3 provided little to no major benefits prior to Skylake. It is true that the X99 platform will hardly benefit from DDR4 3600 vs. say DDR4 2666 but all things being equal, if prices are similar, it's generally better to go with lower voltage DDR4 and tighter timings since those chips are likely to be of the highest quality. A quick browsing session on Newegg highlights some kits that are much better than others using the criteria I outlined.
Luckily, G.Skill is basically beating everyone in the DDR4 market right now by offering the best value and the best timings/memory clocks with the Ripjaws 5 and Trident series which means the choice of picking DDR4 cannot be any easier unless one needs to colour match.
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