Ideally, thrust and specific impulse would gradually trade off during flight, but that isn’t generally achievable. Instead, large changes in thrust and ISP are done during staging.
It's pretty common for the second stage (or core stage, for a solid booster/liquid sustainer configuration) to start at less than 1:1 thrust-to-weight ratio. That seems like a pretty good proxy for "Isp is more important than thrust": you're literally giving up vertical speed that you've already achieved for gains in fuel efficiency. Because the rocket is rapidly throwing away propellant mass, the thrust-to-weight ratio recovers before long, and staging would be advantageous even if the Isp weren't different between stages, but it's still a significant and easy-to-study marking point.
Case: Saturn V
For the Saturn V, the first staging switches over from the massive kerosene-LOX F-1 engines with a vacuum Isp of 304 seconds to hydrogen-LOX J-2 engines with specific impulse around 421-423 seconds. First stage cutoff takes place at about 162 seconds into the flight, at 70km altitude. Dynamic atmospheric pressure is down to about 450 Pa from the max Q peak of almost 34 kPa -- there's almost no air left. The rocket's velocity is around 2.65 km/s, nearly mach 8. The vertical velocity component is about 900 m/s. When the second stage starts, it's firing at about 0.8 thrust-to-weight, and the vertical velocity starts to decrease significantly, but it's already 38% of the way to orbital altitude; the vertical speed actually never increases from that point on.
Specific impulse is so much more important than thrust from here out that the engines switch to a more fuel-rich mix towards the end of the second stage run, giving up 25% of the thrust for a small increase in specific impulse to 427 seconds.
Case: Space Shuttle
Two minutes into flight, the high-thrust, low Isp solid rocket boosters burn out. This is at a lower altitude than Saturn V, around 50km instead of 70km -- atmospheric resistance is still somewhere around 2 kPa. The main engines at this point are producing about 0.9:1 thrust-to-weight with a specific impulse of 452 seconds. Later in the main engine burn, the engines are deliberately throttled down to maintain a ~3g limit for crew comfort and payload safety. Unlike the Saturn V, where the vertical speed never goes negative, the space shuttle does give up some altitude late in the burn.
Case: Ariane 5
Ariane 5 is another solid booster / hydrogen sustainer rocket. At booster cutoff, the sustainer is delivering about 0.8:1 thrust-to-weight at 432 s Isp. That finishes off at about 3g, and the upper stage takes over, starting at only 0.25:1 thrust-to-weight at 446s Isp. With that small engine, the rocket takes a good long time getting into orbit, and loses substantial altitude before it does so.