Hi,
The tough part about Iran is getting the visa but once you've got it is simplicity itself. The country is beautiful, scenery dramatic, monuments splendid, people friendly and food delicious. If you want to rush it though, you could easily cross this gigantic country in less than 72 hours: take a cab from Dogubeyazit to the border at the crack of dawn, formalities should not take long. From there take a minibus or collective taxi or hitch to Maku where buses leave for Tabriz. Jump on the afternoon bus to Tehran and you will be there early the following day. You will most probably arrive at the Western bus station (Garage-e-gharb). Take a cab or to the Southern bus depot (garage-e-janoob) and take the first bus to Zahedan (22 hours trip). Commuting between the 2 bus terminals can also be done by a combination of 2 collective taxis taking you to and from Meydan Khomeyni (earlier Meydan-e-Sepah).
The Zahedan transportation scene is chaotic, try to locate a pick up which fills 4 pasangers and will take you for the 80 km ride the border. NB: long Pakistani siesta from 1:00 PM to 4:30 PM and Pak is in a different time zone.
If you haven't overstayed your visa the border formalities are a breeze. Change roops with the black marketeers but just enough to get you to Quetta where you will find better exchange rates. All transportation from Koh-i-Taftan eastwards leaves as a big convoy around 6:00 PM. You will get to Quetta around 6:00 AM the following day. From Quetta you can take the train to Lahore or leapfrog with buses via Sukkur / Rohri, Bahwalpur, Multan and finally Lahore.
After enjoying Lahore you could take minibus no. 12 from one of the side streets in front of Lahore Rwy Stn. NB: make sure that you take the *right* no. 12, there is confusion inherent to this issue. You might have to change minibus half way. Waga border is also easy as long as your visas are fine.
India. Take a rickshaw to Attari village bus stand and jump on the bus to Amritsar (30 minutes). In Amritsar you are on Indian Railways' national network, India is in the palm of your hand. Enjoy. If you absolutely insist, you could rush the whole trip from eastern Turkey to Amritsar in less than a week. I wouldn't do it.
Any further questions ? feel free !
smiles, yuval.