If someone is called to the Torah when he is in the middle of pesukei d’zimra, he should go up, make both berachos, and also read from the Torah along with the ba’al korai (as he is always supposed to do). He should try to finish the paragraph he is saying before he makes the first berachah.
Attention Gaba’im: Lechatchilah he should not receive an aliyah, unless he is the only Kohen or Levi.
The very best place to daven is in a Beis Medrash where the kol Torah is constantly heard. Next is a Shul where that is not the case: I.e, it is reserved for only davening. It is also preferable to daven with more people, in fulfillment of b’rov ahm hadras melech.
Of course, the speed of the Tefillah must play a role as well.