Highway/motorway speed limit for non EU tourist in Germany [duplicate]

• You nationality is irrelevant as far as German law is concerned. You can go as fast as you want unless there are signs telling you otherwise. Most of the Autobahn has these signs. Especially the Frankfurt area also has lots of radar speed traps. I wouldn't recommend going faster there.
• The "Richtgeschwindigkeit" of 130km/h is what you're supposed to go, conditions permitting. This has nothing to do with a speed limit.
• If you drive faster than the "Richtgeschwindigkeit" and end up in an accident, it is automatically (at least partly your) fault.
• If your vehicle can't go at least 61km/h it's no allowed on the Autobahn (which must not mean that you have to go 61km/h though).
• If you go faster than 250km/h you lose any insurance. Most "normal" (rental) cars will have a electronic limitation of 250km/h. Some tuning companies remove these chips. Unless you're extremely well off I wouldn't do it.
• Unlike many other countries the drivers on the Autobahn are generally extremely disciplined: People are supposed not to overtake in the wrong lane (=right) and to make room when a faster car approaches. This discipline is what enables the no-speed-limit approach. Adhere to it. Do not overtake in the wrong lane. People will not expect this and your chances of getting reported are as high as the risk of a nasty accident.

The reality is that you can hardly ever drive 250km/h or above because someone slower will be in front of you.

German speed limits come in two flavors: mandatory limits, exceeding which is punishable by a fine, and recommended limits (Richtgeschwindigkeit), which can be exceeded as long as you stay in control of the car. This also means that, if you have an accident while exceeding the recommended limit, you have increased liability.

So the answers:

1. Around 50% of German autobahns (motorways) have a recommended limit of 130 km/h, but no mandatory limit. This means you can drive 300 km/h in a Lamborghini if conditions and traffic allow, but try not to end up like this guy. (Who's actually in Hungary, but close enough.)

2. Your nationality does not matter: if you can legally drive in Germany, you can legally drive at any legal speed.

I would put it like this: There is no general speed limit on the Autobahn, meaning that when there is no specific speed limit announced via signs, you can theoretically go as fast as you want (Nowadays though, there are speed limit signs on most sections of the Autobahn). This applies to any drivers, regardless of nationality.

I would however recommend that, especially with a rental car, not to drive (much) faster than the Richtgeschwindigkeit of 130 km/h as mentioned in the other answers. Usually, if you are involved in an accident (even if it is not your fault) and you were driving faster than the Richtgeschwindigkeit, you might get in trouble with the insurance.