Bought the 4x.
Costs at 64x: 2x - 70 (56 with discount), 4x - 132 (106 with discount), 8x - 177 (142 with discount).
Also some info about total multiplier:
Code:
Character Multiplier MinTimeToUnlock MinTimeToMax
Cherry 0.5 0 20m20s
Lola 0.5 0 40m
Sanshi 1 0 10m40s
Ice 1.5 0 11m
Geeky 2 10m40s 50m40s
Dora 2.5 22m40s 20m40s
Frecly 4 43m 40m20s
Pantress 6 1h3m40s 4h20s
This table may help developing a better plan. Multiplier - max base multiplier that you gain from all 10 scenes of a girl. MinTimeToUnlock - required time in Fake It on other girls before you can unlock the character. MinTimeToMax - required time in Fake It on current girl to complete all 10 scenes (I am not sure about Pantress' long MinTimeToMax as I don't remember waiting this long last time, but she has 4 Take Photo Fake Its and I've written that each one takes 1 hour, will need to check this on next reset).
Maxing fastest two girls (Cherry, Sanshi, Ice) gives 3x in 40 minutes. Another 2.5x in 20 minutes from Dora. So 5.5 in an hour compared to 2.2*4=8.8.
A little better way would be to max Sanshi and Ice in 21 minutes, then Dora in 20 minutes for 5x in 40 minutes or 7.5x in an hour on average. But you will get Frecly and Pantress unlocked and will be able to do few of their scenes (8 for Frecly and 6 for Pantress) that don't require dating (Fake It). So eventually this will give 5+5.1=10x in 40 minutes or 15 in an hour on average, almost twice better than that 15 minutes run. This counts only required Fake It time though, so actual total time will be a little worse than 40 minutes or much worse as it will include those 15 minutes for first 4 girls. Still it will be easier to do than 4 resets at 2.2 when you can do each action except Fake It without waiting for skills/money.