Irfan Pathan: Can swing the ball, but doesn't know what pace is. Really struggling with line, length and accuracy, which have to be your bread and butter if you don't bowl fast. He doesn't have a natural command of those things, so he will suck and be out of the team within a year to year and a half. Oddly enough, he actually has a 'slower ball', which would imply that the other balls in his repertoire are fast. Sadly, this is not the case.
Munaf Patel: Has OK speed, but has to learn how to swing the ball better. He doesn't have express speed so he has to increase the type of deliveries he can bowl. Doesn't seem to be a natural fast bowler, so puts a lot of strain on his body. Most likely will struggle with pace, injuries and accuracy, and will be out of the team within 2 years.
Sreesanth: Has the best pace of the three. Still not express, but enough to make the batsman hurry a little bit. Seems to be more naturally athletic so he might be able to add a few KMs of pace, and some muscle for better durability. Really struggles with the run rates, way too agrressive at times. Also seems to get discouraged easily, as witnessed by a couple spells in WI where he couldn't even complete his runups. MIght stay around in the team for 1-2 years, before gradually falling off.
All in all, the overall rating of the pace attack is D+. The worst in international cricket, or close to the worst. Most likely all three of them will be abandoned as soon as the 'next big thing' in pace comes along, and the process will repeat itself until we get a genuine fast bowling star.