Here are my two cents:
1. Quark Turbo X
Pros:
1.brighter than advertised (as expected from 4Sevens) It hangs in their with my 600+ lumen flashlights.
2. Big head gives it quite a throw. 100-200meters, no problem!
3. Readily keeps the two modes you program it to run in.
Cons:
1. you only have access to two modes at a time, you have to program the modes you will be using first (you can relate to this owning several tactical Quarks)
2. doesn't fit protected RCR123 properly. A bit tight on the batteries, you can get them in there, but at the risk of ruining the light or the batteries. What you could do is run them with unprotected RCR123's.
3. does not have low voltage cut off, it will run unprotected RCR123's to zero voltage (the other Quarks dont) *I own a Quark AA so I know this. I ended up ruining two RCR123's because of this.
Olight M21X
Pros:
1. Fits most types of batteries readily.
2. SS Bezel is a nice touch, how i wish the Turbo X had this option.
3. Best thrower among the three you are choosing.
Cons:
1. Limited to three modes and strobe.
2. Tube's a bit thicker than the other two.
Klarus XT11
Pros:
1. The most tactical of the three with instant access to Strobe for defensive action.
2. Double switch for switching the light on and changing modes is a nice touch.
3. Great general light, not exactly designed for throw.
Cons:
1. Could inherit the same internals of its older brothers (PWM). To some CPFer's like me it matters, to others it doesnt, so you'll have to decide where you stand on this one. I own some cheap-o flashlights which use PWM for regulation, it can be quite ANNOYING.
2. Not the best thrower of the three.
3. There aren't that many other cons about Klarus lights, they are built well, even Marshall from GoingGear.Com will tell you one of his favorite lights of all time is the older Klarus XT10 (the older bro of this XT11).
My reco:
Since you seem to be like me who loves lights which can take 2XCR123's or 1x1865's, get them all!
I currently own a Turbo X, as for the Olight model i'll probably get it would be the M3X as I am addicted to thrower lights. M21X is no slouch, but I'm trying to get a favorite model per flashlight vendor.
As for the Klarus XT11, if the reviews on it prove it no longer has PWM, I will get this light too.