Initial ride report:
~20 miles in the dark on wet roads, so I didn't bomb down any hills or anything, but initial impressions are good. I was coming from an older Tarmac Comp (and also have a Roubaix), so I thought I might notice a harsher ride, but it seemed really smooth. I have a longer group ride tomorrow on some rougher roads, so that will be a better test. My primary complaint on my Tarmac Comp was the flex in the front end and the SL4 is night and day stiffer. It's also covered with road grit, so it's got that nice used look now.

I did the bathroom scale test and I think it comes in just under 17 lbs without bartape (but with pedals). That's with everyday wheels and powertap, 25mm tires.

On a side note, I went from a 58 size frame to a 56 for the SL4. I figured I'd get some extra drop and a little shorter reach on the 56 and just prefer the feel of a little smaller frame. I test road a 56, but I didn't realize how much shorter the head tube was because the stem was flipped up and it also had spacers. I've got plenty of drop now! Specialized has a different geometry on the SL4 frames with shorter headtubes. They also come with an 8mm cone spacer vs. the 20mm cone on my old Tarmac. All of those changes amounted to a 57mm shorter "effective" head tube length on my new bike. I'm about maxed out with 35mm of spacers and I'm still a good bit lower than my old bike with no spacers. It felt fine on my short ride, but I may end up "unflipping" it rather than running with all the spacers, we'll see.