Drove to Indian Rocks Beach, FL and back from Birmingham, AL over the holidays, 1300 miles total. Was only able to charge once on the trip. Car burned about 28 gallons of gasoline (44 mpg on gasoline, 46.5 overall including electric - Display showed 51.5 mpg on the trip). Folded down both back seats since only me and my wife traveling. Put the compact spare behind the passenger seat (it fits there well with the hollow part of the spare over the headrest of the folded down back seat - I put a couple of beach towels over it and then let the front seat back until it had a little compression on it). I have the aluminum spoked spare so not too heavy, and stays put there unless maybe I roll the car in a wreck. Overall, though, the car was loaded pretty heavily. About 1/2 interstate at 70 mph, the other half 60-65 mph roads. 200 miles driven in the Tampa area while we were there. All in all, I think it did rather well for a road trip. We drove the return trip without too much stopping (560 miles in a little less than 9 and 1/2 hours).
We did a similar trip from the Bay Area to Las Vegas and back (about 1150 miles total). We also had good experience with the car, it was roomy and comfortable and even the long upgrade on I-15 leading to Las Vegas was not an issue and the car kept 70 mPh easily with three adults on board, although it was a bit noisy.
While my highway trip driving in my Clarity has been somewhat minimal, I've found that easing up on the throttle calms the engine noise by a large margin. I was pulling a slight grade (there's nothing but slight grades in flat Oklahoma!) to pass a 18-wheeler and got up to about 78mph. The engine noise started to become very apparent, so right after I got around the truck I eased up to about 68mph. Noticed quite a reduction in engine noise. Since the engine runs at a constant high rpm ~5500 rpm, it would be very noticeable to drivers who are used to an engine doing a leisurely 2000 rpm at highway speeds.
I'm not sure if you meant it that way, but the engine doesn't run at a constant RPM; it ranges from ~1500 - 5500 RPM as needed. While it's fairly loud at the high end because it's a small 4 cylinder engine engine that's clearly not as optimized/dampened for quiet as some cars, a Honda engine should be able to run perfectly fine for long periods at that speed without concern. I think people are more subconsciously accepting of what they're used to with a pure ICE car -- pressing the gas, feeling the transmission clunk down and the engine surge noisily higher as the car accelerates -- than with the noise being somewhat disconnected in time from what they feel the car doing smoothly with no "downshift" cue.
