Between the 700's-500's BC/BCE, the Ancient Greeks sailed to and founded many strategically valuable towns and cities in lands across the Mediterranean and Black Sea regions; (the majority of these cities were situated on or in very close proximity to the coast). Cities, such as Nice, in Southern France, as well Naples in Southern Italy, were Magna Graeca cities. However, could the Magna Graeca geography have encompassed greater territories and landmasses beyond the Mediterranean sea region?-(excluding the Black Sea region). Could the Ancient Greeks have sailed beyond The Straits of Gibraltar-(Known in ancient times as, "The Pillars of Hercules") and established cities on the Canary Islands, parts of the West African coast, as well as parts of the West European coast and the Southern portion of the British isles?
They had the technology to navigate outside of the Mediterranean, or at the very least their Phoenician neighbors did:
According to Herodotus, a Phoenician expedition sent down the Red Sea by pharaoh Necho II of Egypt (c. 600 BC) even circumnavigated Africa and returned through the Pillars of Hercules after three years.
But like the Romans, the Greeks valued wine and olives. A place where you can't grow either isn't a prime location to build a new settlement.
With respect to your specific examples, they technically did settle the Western Atlantic, in that it likely is Greeks who introduced wine in the Bordeaux region.
The Phoenicians barred the strait of Gibraltar from the Greeks. They controlled the Atlantic Sea trade with Western Iberia and Britain. Britain was especially important for tin. This situation was determined by a series of wars with the western Greek colonies around 600 B.C. The westernmost Greeks were the Phocians of Massalia (Marseilles), who were stopped from expanding westward. Massalia did colonize the northeastern coast of Iberia, though. They had a handful of cities which some have equated to the Delian League. In the 4th century, Pytheas of Massalia was the first Greek to take the Atlantic route to Britain and beyond. It wasn't usable, though, because of the Phoenicians. Alternately, the overland trade route to Aquitania was pursued.