Hi, done that route in November/December last year, and I agree with TonyTea - the biggest and most likely risk that anything will happen to you, is while you´re in traffic.

Iran:
in my view, not so bad, a bit like Turkey (ok, sure its worse than that, but nothing compared to the other 2 countries!).... and the Iranians are quite simply the most welcoming people we´ve met in the whole trip, they alone make the country well worth visiting. Main roads are very good, and once you get used to the fuel card system, its no problem riding through there. Only the area east of Bam is a little suspicious, but police are likely to escort you, if they think its necessary. Might be a lot quicker to go without escorts, but if youre allowed to do so, make sure you arrive to your overnight place well before dark.

Pakistan:
traffic worse than Iran, actually the "system" (believe it or not, they have one!!!) is a lot like India, but maybe not so terribly congested everywhere. The road from Taftan to Quetta is actually very quiet. Theres accommodation in Dalbandin and Quetta, but in between is a long stretch of nothing, and relatively bad/slow road, too, so better time your leaving so you will have plenty of time before sundown. I wouldnt ride at night in that area.
I really liked the Pakistani people (and police, too), they were all extremely friendly. Had to do some welding on our bike´s luggage racks in Quetta, and these guys simply refused to take any money, even though they spent at least an hour doing it. They said "money is not everything"... makes you humble, doesnt it!

India:
The only good advice regarding Indian traffic would be: DO NOT RIDE IN INDIA. It is simply the most mindblowingly chaotic place on Earth to ride a bike!! You can easily get badly hurt or killed in there, and to have an accident there would be very bad, as you will probably be the one they think is guilty. It requires 100% concentration from you, every second, just to survive.
Then again, in time you can get used to it (sort of!) and if you take breaks regularly (we did that every 50kms or so) then it is somehow manageable. But I never really enjoyed riding there, except for some rare moments maybe. Usually its just very slow (and BUMPY!!), and saps your energy like no other place.
Indian people are also friendly, but you will have to cope with a crowd of 50-100 gathering around your motorcycle anywhere you´ll stop, that can get annoying sometimes! In more touristic areas, like Goa, you´ll get very much hassled by people offering all kinds of services, that might start to get to you after a few weeks.