No, the .280 Handi with the 26" barrel is not a light gun. I have a 2.8-10 Aetec on mine, and it's not as "handy" as the other Handis I own with 22" barrels.
That said, I've yet to work out a 160-162 load for it, but it has put 3 145 Speer spitzers into .466" at 100 yds, and that load (a near max load of IMR 4831) has killed my last 3 whitetails at ranges of 50 to approx 225 yds. I will still try the 160s though.
The .280 is a great round, but even in the 3000 fps range with 140-145 gr bullets I don't know if you'd see a huge difference over the .270. The 145 bullets don't "knock as big a hole" as the 165 30 cal bullets I'm used to, but they shoot flatter and certainly did the job.
Rick