An aspherical lens is going to essentially give you a pencil beam thrower. It is commonly used with led's, I dont know if Ive ever seen one used with a hotwire setup however I could be wrong. The reason you need to use a glass lens is because if you are generating enough heat the original plastic lens will melt or severely yellow over time. the flat lens will do nothing, as posted before, to give you better focus. only better light transmission due to the higher value of transparency. the best combination of throw and usable spill beam will be from a SMO reflector, although you will have some bulb artifacts. If you want to smooth out the artifacts with the loss of some throw then use a textured reflector such as the MOP. like wise if you are generating enough heat you will melt the stock reflector, hense and aluminum upgrade is in order. And yes the cammed aluminum reflectors from KD and fivemega retain the focusing ability of the original reflector. hope that helps.
