5w represents its flow at cold starts - the lower the number, the better. At operating temperature, there is no difference between a 0w-30, 5w-30, 10w-30, or even 20w-30.
If your car is mostly driven on the motorway, you should consider following the normal service schedule. 16k km (or 1 year) should be no problem with a fully synthetic.
The owner's manual makes absolutely no mention of changing the viscocity at this mileage or that mileage - this is just one of the motor oil myths that are common on these forums.
Don't worry about 80k, thats just the break in period for Hondas . My dad's 03 VTi is travelling fast towards 280k, and it still runs like a champ. Look at my signature.
Xulfiqar uses Mobil 1 0w-40 in his 280k driven Mercedes with 24k km change intervals - that is in Houston's weather, which is apparently as hot and humid as any southern Pakistani city.
xcel of cleanmpg uses 0w-20 in his 250k+ km driven Honda Accord '05 - all year round in Minnesota.