My own experience has been...
12 months ago I got my Pakistan visa in Tehran. It took 2 days and required an interview with the Pakistani consol who made me promise not to cycle through the Baluchistan area on the Iran / Pak. border, but otherwise no problem. It gave the time I needed, as had I obtained it in Turkey I wouldnt have had time for Turkey (2 months), a month detour into Syria / Lebanon and the 2 months crossing Iran. The LP guide will tell you not to get an Iranian visa extension in Tehran. It entailed another brief interview / lecture about the Baluchistan area, but a month extension from there was easy and ready following day.
Of course nothing is written in stone, esp. concerning Iran, and it can change over-night and can depend on your nationality etc so it would be safer to try in Turkey. The major stumbling block, in fact, is not the Pakistan embassy but your own. You will need a 'Letter Of Introduction' (LOI) from your own embassy in order to apply. Many governments have become nervous of their citizens travelling though Pakistan and refuse to issue them. At the time I applied, the UK embassy was issuing them, but the Spanish, Italian, and German's werent, and those were just the few I heard of. They were only allowed to fly into Pakistan, eg into Islamabad so avoiding the Baluchistan area. They would have had to buy air tickets first to prove this before being given LOIs. Its worth contacting your own embassy in Iran by email to confirm this first. A back-up plan through Turkmenistan from Iran should Pakistan become unviable is another option as this tends to be the prefered route lately anyway. Most of those I met in Iran on bikes were going that way through to central asia. Dont over-stay your Iran visa!! Obvious advise, I know, but I missed the border by 20 minutes as I cut it too fine, was put under house arrest, had my passport taken from me and next day had to pay $70 for a 24 hour extension to get out. Getting out of Iran turned out to be harder than getting in!!
Hope this helps.