kaseri,
What are you looking for? Something small? Something for indoor use or outdoor use?
I've done plenty of KL4 mods. The innovator of the KL4 mod is, as far as I know, McGizmo and I'm sure that he's done more than I have. All of these mods have revolved around replacing the 5W with a 1W or 3W luxeon. This gives you less overall light, but also gives you a more tightly focused beam that affords much more throw with a good sidespill.
I've considered putting an optic into a KL4, but I don't think it's practical. If you want to go with an optic, mod a KL1,2, or 3. Putting an optic into a KL4 will result in a lot of lost mass. This will result in heat problems.
If you want something that will put out a lot of light and have throw, you'll need something that will accomodate a 5W luxeon AND and a big reflector or optic. You can't get this in a small light. The McLux PR head will give you some throw with a 5W, more than a KL4, but will fall far short of that of a 3W. If size is not a concern, I'd mod a
M@g light. Something along the lines of a Space Needle.
If you want something small, then you'll have to choose what you want. If you want the greatest amount of light then you'll have to live with the stock setup and the flood beam. If you want throw, you'll have to sacrifice some output. I usually use my lights outdoors, so throw is what I need. Personally, I'll never go back to a 5W KL4.
A KL4 modded with a 3W running at about 1A is a bright light for what it is. That is, of course, a small, pocketable light. It will outperform most small lights but won't hold a candle to lights with a bigger reflector.
If you could be very specific about what you want, I may be able to point you in the right direction.