the website says 259miles,
Sadly that's the government / whatever comparison figure, not realistic at all
I put some models into A Better Route Planner at 20C with no wind, 70MPH ... probably close to ideal weather.
I picked a journey that was all motorway and distance to destination was close to max range for the [i.e. shortest range vehicle] MX 75D
My MS P90D came up with 340 Wh/mile Range = 217. I would say that my range was 220 miles, so ABPR was pretty close, and I would expect ABRP to be pretty representative for all models.
Bare in mind that your normally overnight charge would be to 90% and, of that range, you will want to leave some "just in case" in the tank - 20 miles maybe, to calculate your normal daily-range.
Of course if you are going somewhere you can charge to 100% shortly before you set off (IMO: its not something to get concerned about, I aim to only charge over 90% if I will then set off within a few hours, and to not leave the car sitting at > 90%, nor < 10%, for prolonged periods).
Right: the ABRP figures were:
MX75D 386 Wh/mile, Range 169 miles
MX100D 386 Wh/mile, Range 229
MXP100D 402 Wh/mile, Range 220
MS75 324 Wh/mile, Range 203
MS75D 324 Wh/mile, Range 203
MS100D 324 Wh/mile, Range 274
Slightly surprised that the Wh/mile, which ABPR provided, are the same for D/non-D ... and that the 100 is the same as the 75 (100 being heavier), so there may be some wiggle-room in there
MS P100D 340 Wh/mile, Range 260
MS P90D 340 Wh/mile, Range 217
If I go on a trip that is more than 160 miles I charge to 100% (even on the perfect Summer's day). Always the risk that I get asked to detour for some errand or other! and on one occasions I was late and on the way there used up 50%, wasn't worried as I knew I was not in a hurry on the way back, but I drove back through torrential rain and arrived back home with only 1% left

for a total journey of 177 miles (temperature was 10C on return journey, very wet, cruise set to 70MPH, dual carriageway 90% of the journey, 465 Wh/Mile)
As a foul weather range test I set ABPR for 5C, 10 MPH wind, and rain:
MX75D Range 132 miles
MX100D Range 179 miles
MSP90D Range 184 miles