I have put together a map of the known bit of info
MAS370
I have marked up the flight plan, the three named waypoints mentioned by various sources and confirmed by Malaysian authorities, the Inmasat angle ranges and the final 40° line.
I have added the known points of info we have, last radio transmission, last acars, last primary radar return, based on their timing and then joined the dots a bit from the last known point to waypoint GIVAL. Comments by the Malaysians say it tracked towards VAMPI, but not over VAMPI.
Based on the last known radar point 200 nm of Penang gives us a gound speed in the range of 420 knots. If I stretch the last known point to 250 nm of Penang it comes back at about 470 kts which I think is more reasonable. The last GS from Flightaware had it at 468 kts.
The possible flight paths are my own supposition, it had to get from the last known radar point at 0215 (local) to the 40° inmarsat intercept at 0811 (local) so the lines reflect approx positions based on a number of ground speeds.