Right, here goes.
Your current Fami is probably about 200, using luxeons as you say.
And yes, I'd agree the Shockwave 400 probably using SSC P4's, which can do up to 200 lumens each when driven hard, but they're likely to be toned down in a plastic bodied dive torch because of heat problems (which I'll come on to later) so 400 may be about right.
P7's and MC-E's produce more light, but it's harder to focus as the emitter die is larger (it's effectively 4 leds in one package), hence leading to more flood. Flood is fine for a dive light in good viz, but when it gets murky it can be a liablity as you get horrendus backscatter from all the illuminated particles in the water. That said you do still get a spot with P7 types as long as you're using a decent reflector, as you see when you come round on Friday Ed.
Thing is it's not as simple as just opening the torch and changing the led's mate. You've got to consider all sorts of things, not limited to the volatge requirements of the led's. They all differ. Your Fami will be driven. That means it will have a regulator between the batteries and the leds that controls the power going to the leds. Change the leds and you'll probably need to change the driver, and you'll have to take into account the power source.
Your FAMI runs of 4 AA's, so presuming (they may not be, may be 2S2P) they are in parrallel you'll have 6 volts to play with, so it may be using a buck or boost driver, if you change the leds it will definately need a boost driver of the right power to keep the leds running at max.
It's pretty complicated to work it all out, I don't understand it, it's related to the volatge forward of each led not just their required input.
And regardless of the electrical side the main issue with high powered led's is heat management.
In metal bodied dive torches the heat is easily managed as they conduct it into the water as long as they are mounted on a decent heat sink which is in good contact with the body to provide a good thermal path.
However plastic bodied torches like the PT will always struggle with this problem, and it's possible that the PT 400 is about as high as that design will go. UK had an interesting solution in one of their eLED light cannons whereby they had a tube in the middle on the lens with the inside open to the water and the leds were mounted on the outside of the tube so they were cooled. All pretty complicated and susceptible to damage and leaking though.
You can get dive torches with single P7's and MC-E's, both cheaply from China
DealExtreme: $81.00 Diving Cree SSC-P7-C-SXO 3-Mode 900-Lumen LED Flashlight Kit (2*18650/4*CR123A/4*16340)(I've got one of each) or pretty expensive but much better built from a few proper dive torch people like Barbolight
Barbolight U15D Flashlight in Underwater Lights,Rechargeable torches from Simply Scuba.
BUT, all that said, upgrading what you've got will not be easy, there's no way your 4 AA's, or however many 18650 lithiums you could fit in the same place, would have enough power for 3 P7's to run for a full dive, and you wouldn't fit 3 P7's in that head anyway, not without hacking the cr*p our of your reflectors which would ruin them.
Fitting 3 XP-G S2's may be doable (if you can find some to buy, XR-E Q5s are easier to get), indeed that's exactly what I wanted to do with my SeacSuc X-Led, but I fell at the first hurdle of opening the head with the leds in! Can't work it out at all, only option I have left is to pump air into it until the pressure makes the glass lens pop out!
