Urgent itinerary help - a few days around Delhi

Dear all

I will be heading to Delhi for a conference in a few weeks. I'm planning to take some time in Kerala AFTER the conference. But I'll also have a few days BEFORE. When I arrive, the friend I'm meeting up with will already be in Chennai.

So the options are: I fly directly to Chennai, and we spend a few days around there in a place like Pondicherry (which I don't know too much about), then we fly back up to the conference in Delhi.
Or I fly directly to Kolkata, where he would meet me, and we work our way back to Delhi via Varanasi by train.

Considering the short amount of time -- I will have four days before, he three -- I think it may be a bit ambitious to get from Kolkata to Delhi, stopping in Varanasi. My friend thinks it feasible (basically two overnight trains in a row), but I think it wouldn't be doing either place justice. Kolkata is convenient in that I can fly there directly, and he has a direct flight from Chennai, but it seems too far out from our final destination of Delhi just a few days later. I also think two 12h tains would be exhausting within the space of a few days. How much time do people recommend in Kolkata and Varanasi?

So I guess my question is: where would you spend a few days if one person was coming from Chennai, the other could fly direct into Calcutta, Chennai, or Delhi, and both needed to wind up in Delhi a few days later ?

I should mention we've both already been to Taj and Fatehpur Sikri, as well as Jaipur and Pushkar, though not Udaipur (yet another option, I suppose).

Thanks one and all for any advice ;-)