yes, i use 18 or 35W on the road, and adjustable at home.
20W is more than suitable for any work on motherboard. there are
smaller irons as well (12 or even 8 watt).
40W is ok for experienced (fast) guy. also tip size should match the type of work.
standard tips of irons from hardware store are usually too big for just about
any work on motherboard. might be ok for power section (larger caps, switching transistors) but that's about it.
60W or bigger is good only for soldering larger objects (really large wires, pipes...).
if components has only two wires such as resistors and caps, it is usually enough to apply slight pulling pressure on part while melting solder.
you might have to alternate between two ends until part comes out.
be carefull not to burn pcb. with larger conponents with multiple pins
you could try help of suction cap or other devices (som guys use braid,
heat gun etc.) but this will depend on type of component and how delicate pcb is.
as always, practice makes master so before you destroy something,
try practicing on something similar that is expendable...