now bottom line is this.....your well u max out your Fuel
efficiency depends on yr vehs powerband....(MH2 yea u are right abt
this one) now:
Bigger displacement engines have more torque in the lower RPMS
as opposed to smaller displacement engines so therefore when
crusing @ top gear maintaining revs @ like 2-2.5K rpm is kinda
okay...unlike my 1.3L car which has to maintain @ around 3-3500Rpms
same goes for shifting.....for bigger displacement engines having a
fatter torque curve @ the lower RPM range allows lower shifting
points so please dosent mean that the lower u shift means that the
lesser fuel u'll consume...cos if yea not in the powerband(too low
a rpm) yr car will bog down and u'll have to depress more on the
accelerator(more fuel) and the engine also has to overcome more
inertia(again more fuel) so just go home and read the brochure abt
the specs of your car...they dont print out the figures for
nothing....and Nox,2-3K rpm no engine would sound like outta
breath....its how the engine is designed(i will not go into details
of cam duration,valve lift ,ignition timing and fuel pressure here)
unless u're talking abt a china car...which runs outta breath at
whichever RPMS 
for a 1.6L car 2.5K-3 is the optimum...2K is
too low man...when yea in the next gear it'll be like 1k plus RPM
and the car will bog down....the only factor which wont make it
happen is having a close ratio gearbox...something which is not
favourable in street cars....so yea...
tofu if u have might noticed... all along i am speaking with
reference to cars in the 1.5litre and 1.6litre range... so my
estimate of 1.5k rpm to 2.5k rpm is to me acceptable
and i drive an altis... above 3k rpm in rev i feel that its
breathless... maybe this kinda thing is subjective.... but i always
felt tt the 3ZZ-FE is designed for cars to rev from sub 1rpm when
idling to 3 rpm when accerlating... for maximum efficiency...
why do i say this? the max torque of the 3ZZ-FE is at 3800rpm..
according to what u are saying is true... then the powerband for my
engine is ard 3000-4000... but the ECU prgramme it to shift
up at less than 3krpm everytime.. unless i totally floor it... my
car confirm dun have close shift ratios nor veh high final drive...
it has only 4 gear ratios... having the abover 2 characteristics
will cause it to be extremely inefficient when crusing at speeds of
around 100km/hr...
which brings me to the point of fuel consumtption.. i still
stick to the stand tt the lower rpm the less fuel consumed... it
makes perfect sense... less combustion per minute less fuel
consumed.....
though ur engine might be overcoming inertia with less
torque...doesnt mean it is consuming more fuel.... it juz means tt
less torque is used to overcome inertia.. hence u pick up speed
slower... it will consume more fuel only when u step harder cos u
cannot stand the slow accelration....
which also explains why in stop start situations u consume more
fuel than in highway cruising.. i dun quite agree with ur
explanation as above... what is the case is that when stopping and
starting.. more often than not u are revving to 3krpm and more if u
floor it... but if u are crusing ... most of the time u are doing
1.8krpm to 2.5krpm...hence this explanation coincides with what i
have said in the above 2 paragraphs...
as for why ur car requires higher rpm.. its cos 1.3 litre
produce less torque so u feel the need to utilized max torque
everytime u accelerate... and also perhaps ur engine is an
oversquare engine.. which has a shorter stroke and hence
sacrificing the low end torque... as to why u need to maintain
higher revs at crusing is also partly due to ur engine being an
oversquare engine and partly due to power output...
which brings me to the next point... doesnt mean bigger engine
have lower shifting point.. this is generally the case... but
sometimes there are exceptions... like honda's b16a and b16b
engines which have a max torque of 7k rpm and redlining at 8k
rpm... sure u might attribute to it being vtec... but also partly
due to the fact that the engines are oversquare engine... being
bore larger than the stroke... (source: http://g-speed.com/pbh/b16a/index.html)..
so engine design also plays a part... 
