You really want to compare lbs/min instead of CFM.
I'm seeing 52 lbs/min from an HX and 98 lbs/min from a 75.
52 lbs from an HX? seems overzealous
And yes, double the flow... but you need to watch where you're picking the mass flow rate relative to the pressure ratio on the different maps. Peak flow for one may be at twice the PR on the other.