I believe you said that the hard mode on the 742 was x250, and I believe that is so so fast for a mode that is considered hard. It'd only take a day and a half to max an accounts combat stats (which is really fast).
Whilst I didn't play the hard mode I can give insight on OSRS exp rates from levels 80 upwards
Melee 60-100k/Hour
Range 40-60k/Hour
Magic (alching) 80k/Hour
If you really want a mode that is realistically hard and cannot just be completed in a day:
30x exp: It would take around 5 days at 8 hours per day to max combat stats (excluding prayer)
40x exp: It would take around 4 days at 8 hours per day to max combat stats (excluding prayer)
50x exp: It would take around 3 days at 8 hours per day to max combat stats (excluding prayer)
