I think Egypt would be a poisoned chalice of sorts for the Athenians. Any peace settlement that would leave the region in the Athenian sphere of influence would essentially shut the Persians out of the eastern Mediterranean to an even larger extent than OTL, and the hit to the prestige and authority of the Achaemenid monarchy could be significant. Artaxerxes and his successors would probably view the peace more as a truce than they did IOTL, and although this doesn't mean that they would jump at the first opportunity to declare war on Athens, we might see the tense peace of OTL be even more dominated by incidents between the two powers, such as more active Persian assistance to members of the Delian League seeking to break away (like the Persian actions during the rebellion of Samos), and the Athenians responding by providing more assistance to rebel satraps in Asia Minor and establishing its presence in areas which would nominally be under Persian influence - like the northern coast of Asia Minor, or in Syria and Phoenice (in order to establish buffer zones protecting their new ally).
Even if the Athenians avoided disasters like the defeat in 454 BC which cost them a third of their fleet, the need to maintain a naval presence across the entire eastern Mediterranean and perhaps commit troops to help defend Egypt against Persian attacks would place the city's finances under serious strain, as well as potentially overstretch its military resources, thus leaving it more vulnerable to attacks in mainland Greece. An Athens in control of most of central Greece and with a large presence in the Peloponnese would be simply unacceptable to Sparta, thus creating even more commitments for the Athenians without any guarantees of local support. An Athens on the other hand willing to focus on the Aegean and the Mediterranean and forego any (overt) ambitions aimed at central Greece and the Peloponnese, and more diplomatic, combined with the conservatives and pacifists in Sparta playing a more prominent role might produce a somewhat durable understanding that could allow Athens to focus somewhat unperturbed on Persia; but I think it would be very difficult to prevail over both Sparta and Persia. And of course there's the question of the relations of Athens with the new Egyptian state, since the existence of a common enemy (Persia) wouldn't remove all the potential grievances and disagreements that could arise between the two powers.
Even if the Athenians avoided disasters like the defeat in 454 BC which cost them a third of their fleet, the need to maintain a naval presence across the entire eastern Mediterranean and perhaps commit troops to help defend Egypt against Persian attacks would place the city's finances under serious strain, as well as potentially overstretch its military resources, thus leaving it more vulnerable to attacks in mainland Greece. An Athens in control of most of central Greece and with a large presence in the Peloponnese would be simply unacceptable to Sparta, thus creating even more commitments for the Athenians without any guarantees of local support. An Athens on the other hand willing to focus on the Aegean and the Mediterranean and forego any (overt) ambitions aimed at central Greece and the Peloponnese, and more diplomatic, combined with the conservatives and pacifists in Sparta playing a more prominent role might produce a somewhat durable understanding that could allow Athens to focus somewhat unperturbed on Persia; but I think it would be very difficult to prevail over both Sparta and Persia. And of course there's the question of the relations of Athens with the new Egyptian state, since the existence of a common enemy (Persia) wouldn't remove all the potential grievances and disagreements that could arise between the two powers.