W5W for the clear lens is OK.
You will be OK; the 5 watt W5W bulb is the correct one for the front facing clear lens section of the headlight assembly. Some guys are using bulbs with the silver coating just for daytime looks. I would tend to stick with the LR supplied bulb however.
Re melting, it is the sidewards yellow and at the rear, the red "clearance" lights that require the cooler W3W bulb. Actually these sidewards bulbs may be good candidates for LED bulbs as you cannot see the bulb and the amount of light and colour does not matter much.
One has to be careful about where one puts a LED bulb however as sometimes the diagnostics of the computers picks up the LED and sees it as a fault. This is particularily true of the signal light, tail light, and brake light bulbs. For those, I suggest you purchase genuine LR bulbs as off shore or LED can really foul up the computers.
The file re the P21/5 bulbs in the link below may be of interest.
http://www.**************/gallery/thumbnails.php?album=5082
Where the ***** is, insert
disco3 co uk and insert a period in each of the two spaces.