Xbanker,
By all means go with the P-61 lamp is a tremendous improvement in brightness and in the area of illumination (The hot spot is bigger) which will aid you when you enter a room to clear it.
The throw remain the same, due to the reflectors been the same (heavily stippled) the reflector is designed to provide a quality beam without holes or artifacts with a very good flood or side spill.
For a weapon light to be mounted in a rifle a smooth reflector will give you more throw.
As an example I have several TACM III mounted on my long guns that have a lot more throw. (70 yards opposed to about 45 for the Surefire) this is due to the reflector been slightly bigger but smooth, not orange peel.
When you get to light with the intensity of over a 100 lumens the artifacts disappear at a few yards range.

You will be happy with the 120 lumens lamp on the 6 P because it is more intense and you will start seeing the white light that Surefire talk about.

The more lumens you put out the more you are going to see and the bigger area that will cover, an P-91 lamp (200 lumens) in a Surefire 9 P or C-3 is a revelation, and from that you will want to go to bigger things like the Surefire M-4 or M-6, (350 lumens and 500 lumens)

Let me show you the relationship in brightness between those lights, lets start with your Surefire with the stock lamp (P-60, 65 lumens)

Surefire P-60 65 lumens



Surefire M-4 350 lumens



Surefire M-6 500 lumens



And now the most powerful flashlight in the world (which I made) the MAG 951 (951 lumens)



NOTICE:
Lumens can be additive and hazardous to your wallet!!

Oh, but it is so nice to have in your hand something that will really blind your opponent!!!!

The biggest advantage is the lack of need of panning the room with your light, a Surefire M-6 at 500 lumens will let you see everything around (more so the MAG 951, that have the advantage of been rechargeable as well as double the lumens).
Both are fantastic lights to use against dogs that chase joggers, the critters are scare of the light and will be blinded by it.
The normal reaction on them is to stop and not move; because they are positively blinded they don't move as they can not see where they are going.
More or less same reaction than deer exhibit when you approach them with your car in the middle of a road.

regards
black bear