I think that those engineers at Inmarsat and the AAIB (UK Air Accidents Investigation Board) would disagree with you ... :-) ...
If the plane flew for more than 7 hours, where is it and what is happening with it? 554.4 mph x 7.5 hours = 4,158 miles of feasible flight. The distance from Malaysia to Iran is 3677.58 miles (481 less miles). It could have lowered its airspeed to look like a civilian aircraft. Below 10,000ft there is a speed limit on jet traffic in the United States. No civilian traffic can fly faster than 250knots (287.695 mph). A 777 has no problem staying in the air at 250 knots. Perhaps Flight 370 flew below 10,000 ft to avoid radar detection and slowed down to 250 knots to appear as a civilian aircraft when radar detection was possible. An alternative idea is that Flight 370 flew at an arc to move as far away from India before it went north to Iran. That must have added flight miles to the 3677.58 miles.