SpaceX Thought experiment -a Saturn V class vehicle within 10 years?

The new update at SpaceX has got me cogitating.

After Falcon V development is complete (LEO throw weight ~13,000 lbs,
GTO 4200 lbs), SpaceX will have a Merlin 2 engine with a sealevel
thrust ~100,000 lbs, enabling SpaceX to compete against the lightest
versions of Delta IV and Atlas V. Falcon V in that configuration would
have a GLOW ~500,000 lbs.

The next obvious step would be a Falcon X, which would compete with the
heavier versions of EELV (~30,000 lbs to GTO), presumably with a GLOW
~1.5 million lbs. With 5 engines like Falcon V, 'Falcon X's' Merlin 3
or whatever would need ~300,000 lbs sealevel thrust. Then you have a
third generation vehicle with a third generation engine-- and nowhere
to go with it.

If, on the other hand, you take SpaceX at their word that they intend
to develop a ~1.5 million lb thrust engine in the next few years,
perhaps there will be no 'Falcon X'

Instead, a bigger version of Falcon I, call it 'Gigantor I', with one
Merlin 3 at 1.5 mil lbs thrust, as the lower stage. You probably save
some weight in the stage with one engine, with similar reliability to
Falcon I but the ability to carry heavy payloads--and no solids. Assume
the 1.5 mil thrust engine costs 3 times as much as the Merlin 2--
still you're at 25 mil for the Gigantor I engine.

Now put 5 Merlin 3 engines on the lower stage--you're talking about a
vehicle with GLOW of 7.5 million lbs. Now you're dealing with a Saturn
V class vehicle (Gigantor V), with the ability to put 150 tons in
orbit. Perhaps for a recurring cost of less than $200 mil.

thoughts?
cuddihy