Is going fast in atmosphere worth science?

[Kerba Fett]

You get science for orbiting, for your first suborbital flight and lots of other stuff around Kerbin.

I was wondering if there's any point to unlocking better jet parts other than for launch boosters.

Playing in the sandbox I managed to hit 2225 at 25km. If I could get orbital speed in the atmosphere in career mode would I get any science for it?

[Streetwind]

Nope, but there are science instruments meant for use inside the atmosphere. Namely the barometer and the sensor array nosecone. The thermometer also works, in contrast to space (where it only works when being landed on a celestial body). So you can get a number of science points by exploring Kerbin's biomes with your plane.

[Tex_NL]

Streetwind is correct, there is no extra science to gain by going faster. But 2225 m/s at 25km is a worthy achievement. This kind of speed and altitude is what you should aim for before you switch over to rocket power when launching an SSTO.

[Geschosskopf]

Don't forget the atmosphere analyzing nosecone science part, which does something in addition to the regular instruments. So a bit of extra science there.

Anyway, going fast in an atmosphere can actually be counterproductive. If you have orbital velocity, it counts you as being in low orbit even if you're in the atmosphere, so you can't sneak in atmospheric science during aerocapture/braking passes, unfortunately. So to get the "flying over" science, you have to be below ortibal velocity.

But note that you don't have to be actually flying to get "flying over" science. Hovering, dangling on a parachute, or doing a short hop off the ground counts as well. Even an EVA'd Kerbal still hanging onto the pods hatch counts as doing an EVA report while "flying over" whatever terrain you're landed in.