Also, how much are you willing to spend? One good option that comes to mind are Vin's P60 XML dropins being sold over in the MP. (Around $40) I have one and it is super bright, but the run times are not all that long. Since you mentioned that as a request, then Malkoff's seem like a better choice. The Malkoff lines work like this..
M61 - standard dropin for a p60 host. It will get you 260 lumens for about 2 hours off of 2 batteries, that will be pretty close to full output then it will dim and continue running for 1 more hour.
M61L - The L stands for longer run time, but at the cost of lumens, or output. It does 175 lumens. This will run for 5 hours on full output, then 7 hours till dead.
M61LL - This will run the longest but has the least output. This light engine will put out 100 lumens for 10 hours. This will be less than your P60L but will run far longer. It wont die for 16 hours.
All of these can also be had in "M61W" format. This just means that the tint of the beam is warmer, closer to incandescent like light. The output is a tiny bit less but its more a feature of how our eyes work. Many people find this colored beam more natural and it allows them to make out objects clearer, especially outdoors. Also these tints, or all tints really, are measured in a kelvin scale. So when you see something like 3500K for a light, its referencing the color according to a kelvin chart. The lower the number the warmer the beam.
There is also the M91 and M91W. These are XML based dropins that Malkoff sells and they are far more floody than the M61s. They light up a very large area but they don't throw as far, or last as long. They are impressive however. The M61s are based on the XPG Led diode. The XML is newer, and physically bigger, so it puts out more light. The weird thing, is that the smaller the diode is the further the LED will throw the light. So basically in all lights you see today you will just see XPE/XRE, XPG, and XML. XMLs are the newest, XPGs are still plenty popular but fading due to the enhanced lumen output of the XMLs, and the XREs are still used in lights where you want throw. M60's had XRE's, M61s have XPGs, and M91s have XMLs.
Also if you stumble across the M31s/M31Ws these are just intended to be run off of one battery. Or 2 AA batteries. Voltages are important for light engines as it lets you know what kind of battery to use. The 6 in the M61 means that it runs off of (2) 3 volt CR123 batteries. It can also handle more however, up to 9 I believe. That is why its rated at 3v-9v. That way you can run it off of 2 rechargeable batteries, which typically run at 3.7 or 4.2 volts. The M31 series however only runs off of 1 CR123 battery, at 3 volts.
Also be wary of lumen ratings. The higher you go typically the less run time you get. Also it just depends upon the beam. Those lumens are either tightly packed into a throwy beam, or spread out in a nice wide useful flood beam. The M61 series tries to accomplish both, and it does so quite well. The previous line of Malkoff's were the M60 series. They had an optic and would throw their beams of 235 lumens further than the new M61's, but the beam isn't as wide and useful, nor does it last as long as the new generation.
The difference with Malkoffs, and what you pay for, is that they have a phenomenal warranty, should you ever need it, and they are built like tanks. The one thing that will happen to your 6P is that it will be heavier. The Malkoff's come with a massive solid brass heatsink. This heatsink is potted which means its filled with this material that makes sure everything stays in place. These things are the most reliable, solidly built dropins out there. I just sold one the other day so I have a picture of it, (I have like a dozen of them so it was just redundant). Malkoffs new run around $50-70, or 80-90 for M91s, and can be found used on the marketplace or new at Malkoffs site. Either way, buying one used its just as good as a new one because of the excellent lifetime warranty they have.
That being said, Nailbender also makes some good dropins. You can also get some cheap dropins from the DX/China route but dont expect them to last long or put out what they claim lumens wise for more than 2 minutes.
Hope that helps.