Is 27 horsepower actually enough for daily highway riding?

Rode a 300-class single as my daily for two years, about the same commute you're describing, 20-something minutes at 65. Here's the honest picture: it'll do the speed, but it sits pretty much flat out the whole time. Around 8,000 rpm, buzzing your hands numb, and any hint of headwind drops you to 58 and you're just sitting there watching cagers drift past. It's not sketchy, the bike is stable enough, it's just relentless. There's no gear left. No burst for passing the guy doing 62 in front of you.

Gonna push back on the 'stable enough' part. My experience with a light single at sustained highway speed is that it gets shoved around way more than the guy above makes it sound. Every box truck that passes you shoves the front end around, and crosswind days are genuinely tiring because there's just not much mass holding a line. Maybe his roads are sheltered, but around here that two year commute would've worn me down worse than the buzz did. Worth the OP asking whether his route has open stretches or bridge crossings before he commits.

Yeah, the guy talking about crosswinds is dead on from what I've seen. My old 350 single got pushed all over the place whenever a semi went by at speed, and I remember one day with a steady side wind I basially had to lean the whole way there and back. What sealed it for me was the gearing, honestly. Mine was geared so short that highway speed ate up half the rev range, so there was nothing in reserve when I actually needed it. Coming from a bigger twin like you had, that part takes the most getting used to.

I teach rider courses, roughly 200 students through my range every season, and the small-displacement question comes up constantly. My take: skip the passenger idea entirely, that's a non-starter on a 27hp single at 65. One-up it's fine, two-up you're down in the rights lane with semis stacking behind you and that's when people make dumb decisions. Also, your old 650 twin is a bad reference point. A twin masks a lot. Take the Harley for a test ride on your actual commute route, into the wind if you can, and you'll have your answer in 25 minutes.

One thing I'd want answered before putting money down is the service schedule. A single running near its rev ceiling for a half hour every day is a very diferent machine at 15,000 miles than one poked around town on weekends, and small engines in that class often want valve clearances checked at intervals that get genuinely annoying once the bike is your daily commuter. I'd also ask the dealer what speed it actually does in top gear at a sane rpm, because a lot of these little bikes are geared for fun on backroads, not for sitting at 65 all morning with anything left in reserve.

Update: took one for a test ride anyway and wow, the replies were right. Flat out the whole way at 65, hands buzzing, and a box truck went past and moved the front end enought that I bailed on the idea entirely. Also the instructor's point about passengers settled it since I occasionally take my kid to practice. Kept shopping used instead.