After the last drone ship landing, I collected some video screenshots from every successful recovery attempt, right at the moment of main engine cutoff and first stage separation. The screenshots are sequential from ORBCOMM-2 all the up to today's THAICOM 8 launch:
Falcon 9 first stage velocity and altitude comparisons
These four screenshots show Falcon 9 velocity and altitudes at the approximate moment of main engine cutoff, just before stage separation. From top: ORBCOMM-2, CRS-8, JCSAT-14, and THAICOM 8.
This gives you an idea of how much the difficulty level has increased with every landing success. These screenshots aren't perfectly accurate—and this also assumes the displayed telemetry matches what's happening in the video—but it's close enough to illustrate how much faster the Falcon 9 has been traveling during the last two flights. Those payloads were headed to geostationary transfer orbits, which requires a lot more speed and energy than low-Earth orbit launches. Here are the numbers:
Speed at MECO/separation, km/h (estimated)
Altitude, km (estimated)
The table also shows you how launch trajectories vary depending on orbital destinatination. Notice how the first stage burn for low-Earth orbit puts the rocket at a slightly higher altitude.
As far as THAICOM 8 is concerned, you can be sure SpaceX has more pretty pictures and video on the way. Keep an eye on their Flickr and Twitter accounts for more.