Well 351's were never known for 'great mileage' and acutally 9.5 to 11 sounds about right!
But I see you got the point! Matching the cam profile to your expected cruise rpm helps to optimize everything, including gas mileage. But of even more concern would be drivability issues. If the motor is not 'comfortable' you have to give it more gas than you would like, or consider down shifting, or speeding up, all of which is a hassle and distractes from the enjoyment of the cruise.
I'm not saying the Comp Cams 282S is right for YOUR motor, but that basic profile makes for a nice 'lumpy' (sounds mean) but reasonable idle. It pulls well from 2000 (even lower) but maxes out around 6000-6200 which might be to low an rpm for some. It's a solid flat tappet, some prefer a hydraulic or hyd roller. I would NOT recommend a solid roller unless your willing to spend BIG bucks and get the absolute latest technology using
oil pressure feed to the rollers (read $$$).
Matching the components, ALL the components including trans gear ratios, ah, THERES the ticket! You really do need to consult with the best engine builder you can find (uh, that aint me).
I am a grasshopper at the feet of the masters!