The longer the haul, the thicker I'd choohse my tires, for comfort. I'm more of a 15-minute miracle than an endurance type, but have done at least one mile-century on the Big Apples, and they definately hlped my soft lazy ass get through it. It's also pure fun how I get to take short cuts like I would on an XC bike. When a cyclepath continues on the other side of a road, I don't take the two shart 90º turn, but cut across the grass shoulders and curbs without losing momentum.
I rode up Alpe d'Huez with Big Apples in 68min iwth a silly long warmup on the first cycling day in weeks, and didn't feel like they were holding me back (down). Comparing rolling resistance to friends on 23c professional road racing tires, I'm not losing out, really. Over 45km/h perhaps air drag becomes unfavorable.
I've now done 2 weeks of straight commuting (10mi single trip) on the SS 42x16 Cross-Check with 2.0 Apples, and one week on the geared Fisher with creaky ISIS and frankengears, 2.35" Apples. The 2.35" actually give a higher top speed down a tunnel I cross, where I let the bike find it's terminal speed where air drag+rolling resistance cancel out my lazy ass's weight. Odd, as I roll over 42km/h there, 44km/h for the 2.35's, you'd expect air drag to become a bigger factor. My aero position on the Fisher with trekking bars may just be better.
In short : slick tires are the only place in cycling where bigger really always seems better to me.
Before the BA's, I rolled Continental Sport Contacts in 35 or 37. They felt like they rolled super fast, and they were like 540g I seem to remember. Not the grip I was looking for on wet pavement though, I never dared push. I a straight line they were awesome, but definately less comfortable than the BA's.