Speed limit still exist.
Oh, and you can't orbit any celestial object.
"Real physics" yeah.
Dude, you are ALWAYS orbiting. Orbiting is why the speed limit exists. The Nav beacon orbits the sun, the planets orbit the sun, the stations orbits the planets. Every single little marker you drop out of supercruise into is orbiting something it just doesn't look like it.
And the speed limit is the maximum speed your ship can achive while using thrusters to counteract the Gravity - Centrifuge inbalance caused by you traveling x00m/s faster than the orbital speed.
Your speed is always relative. Orbital physics exist, it just the space ships of 3300 deal with them automatically. If you want to mess with orbits go play KSP