Not a fan of the gas irons; they always seem to have the hot gas outlet from the mantle in the wrong place for me, sending heat over places I don't want it to go!
The iron needs to have a good size tip. That means at least 6.5mm diameter with a single diagonal cut. It is the ability of the tip to hold heat that is the key to good joints in a short time, not just the wattage. Weller make a
soldering gun with a copper 'wire' tip. It is rated at 140W, but is useless for motors and speedos as it loses heat from a very small tip so fast that it can't melt a larger joint.
As Traffman says, buy a good one once! The best on the market are
Weller and
Antex and both do 12v versions if you prefer. The 12v ones will also work well with a power supply of 5 amps or above.
Both these will make soldering motors and speedos very easy, although you do need to practice. Try using a smudge of paste flux (never acid flux!!) to make the job even easier but don't fogey to clean it off the joint afterwards. It doesn't do any damage to leave it, just looks grubby on your new install. HTH
