I finally received the timing certificate from the Mumbai marathon organisers.
My final official finish time was 4hr 22min 13 seconds. The splits were as follows -
14.1km - 1:14:24 @ 11.22km/hr
23.2km - 2:05:12 @ 10.44km/hr
32.5km - 3.07:57 @ 8.53km/hr
Finish - 4:22:13 @ 7.47km/hr
So as you can see the final leg is what killed the excellent pace set during the first half of the run. The pattern is quite similar to the way I ran the Singapore run (it was aconscious decision and with the Bombay heat this was the only option). So had I been able to run the last stretch (beyond 32.5km at the earlier pace of about 9km per hour, I could have easily finished with a time of sub 4hr 10mins (only if that silly knee pain had not happened). But, there is always a next time and I plan to make the most of it.