Power consumption is calculated at amps x volts, and the higher Amp hour (Ah) capacity a battery has, the longer it will last.

If you're using a higher voltage battery then you need less current to get the same power output. So, for example's sake, let's say you're using a motor that's capable of 2000w power.

2000w / 60v = 33.3A

2000w / 52v = 38.4A

2000w / 48v = 41.7A

Less current being used means more range, so the difference in Amp hours you mentioned between differing voltage batteries is negligible really. The long and short of it is, the less current your motor demands, the longer your battery is going to last.

Of course in the real world you're very rarely going to have your bike motor running at that constant unvaried RPM for the entire duration of your journey, but it does give you a rough idea.

I can't remember the exact figures, but there is a point at which motor efficiency and speed increases really go out of whack. By which I mean it takes a certain amount of power (watts) to get to a certain high speed, and then anything past that requires far more wattage to achieve the comparable increase in speed. It's all down to drag and aerodynamics and so on. Hopefully someone with more technical/theoretical knowledge can jump in here with a link or something (I don't even know what words to search for).

Basically it's something like, it would take 1500w of power to get up to 20mph from 0, but then going up by 10 to 30mph would require another 1500w? So it becomes a case of diminishing returns where the extra power isn't necessarily just going into propelling the bike forward, but also going into counteracting the extra resistance/drag that comes with much higher speeds. Does that make sense?

ETA... The trade off for higher voltage and less current is that you need to use more cells in series to make up the extra volts, so a 48v 15Ah (13s3p) battery using 5Ah 21700 cells uses a total of 39 cells, while a 60v 15ah (16s3p) battery uses a total of 48 cells.

Alternatively, using 52 cells in a 48v 13s4p configuration, so just three more than the 60v 15Ah version above, would give you an extra 5Ah of capacity/range... But at the expense of using more current to hit higher speeds.

Ultimately it's a fine line between riding to ride as fast as possible... And riding sensibly and safely at more reasonable speeds and getting a lot more longevity out of your battery. Making no assumptions on your situation or use case, but I do see quite a lot of posts from people in here who basically want to turn an analogue bicycle into a Harley Davidson.

And while it is technically possible to do so, and to achieve shockingly high speeds, is it really necessary, or safe, to do that? Probably not. If you come off a bike at 25mph it's going to be very painful. If you come off at double that, or even higher, it doesn't bear thinking about.