My experience with a 150cc is that tthey are slightly too small to get the rpms down to 2k when going 40mph. If you'd be able to do that, acceleration will suffer.
Most 100-150cc engines come with a 4 step gearbox, or a cvt with similar gearing, set to reach 4k rpm at 40mph. Theoretically, in order to achieve the same gas mileage and performance, you'd have to halve the rpm, and double the cc, which would translate in 200-300cc for 2k rpm.
The good thing about 250ccs is that they come with a 5 step gearbox.
Some even a 6 speed gearing. Those 6 speeds are the best, but very hard to find on smaller bikes.
I much prefer a manual gearing over a cvt, because you have more control over mpg and performance than on a cvt, and it brings an additional bond between rider and bike.
The only 2 reasons for not yet diving into the rebel, is that a cruiser-styled bike does not offer much pprotection against the rain, like the klr does. The klr has small fenders, that keep the legs relatively dry from rain. But also the high price.
I will still keep my evo with flat floorboard for groceries, another reason why scooters are the better option.
Im still looking for the perfect scooter. A chain driven 200cc scooter, with semi automatic gearbox.
Good for a sprocket change, unless it has 6 gears;
Basically an automated gearbox, with shifter buttons, much like the Honda NC700x would be the ideal gearing setup.
For my long distance rides, and daily travel, I'll use my Elio car, and will get rid of my regular car, saving hopefully ~$130 a month on insurance cost, and ~$40 a month on gas.
Which will come down to ~$2000 of savings per year with my current vehicle, or ~$3000 per year with my friend's car.
I still have until the end of the year, to save up $9k, if I do my best, it'll be possible, probably getting a good $6-8k back for my car, and $2k back for my Honda vt750 motorcycle.
I'm not too fond of cruiser bikes, I much prefer something more modern, like a naked bike, but it has to be comfy, without getting the feeling like they cut corners on the 250cc models, like what they always do on base models (eg:no tach, lousy gearing, hard suspension,...)
For that reason I prefer the Rebel 250 over the Suzuki tu250, because it's more sturdy, same gas mileage, more comfy, softer seat and suspension.