By the time I finished that second set, a couple treadmills were open, so I grabbed one. Either I wasn't recovered from lifting or I did something stupid with over-breathing, or some combination of both, so my first mile just sucked. Once I straightened my head out, I got in a mile at 6.0 or 6.5 (I tweeted 6.5, but in the clear light of morning I'm finding that a bit hard to credit). At the 3.3mi mark I felt like I hadn't done justice. I was at or more likely a bit past 45 minutes, so I decided to shoot for a full hour. In that overtime is when I got in a couple half-laps at 8.5. Total distance: 4.5mi in ~60 minutes.
I also feel like I'm coming up against the law of diminishing returns, which is to say, I think my progress curve is leveling off because my session time is decreasing. I've considered this a couple times previously but didn't take it to heart. Now that I've reached a point where a 5-mile session in an hour or less is realistic, and I can take miles and more at a moderate jog, I think it's time to ratchet up session base distance.