I recently received both, and in the same package! It was a long wait for both, especially the L5, but I'm very happy with both lights. Anyway, here's my opinion. . .
The T3 is an impressive light. . . fairly compact, and with great throw for a light it's size. Mine is quite white. But like the XO, it has a somewhat "ringy" beam, kind of reminding me of Saturn. It feels great in the hand, and I like the clickie switch. It can still be locked out via the tailcap. I expect it will have more runtime than the L5, but some of the flashlight review sites will probably tell more about this.
The L5 puts out more light than the T3 by a considerable margin according to my eyes. It has a very distinct center hotspot and a very wide flood area. I would say that it's "throw" is about the same as the T3. . . but what a difference in the beam! The L5's beam is PERFECT. . . not a ring or artifact in sight. It's not surprising that more light comes out of it either. I think its a 5 watter, vs. three for the Inova. But, you can buy TWO T3's for the price of the L5, and still have some left over. That may be compelling for some people. The L5 is beefier and heavier as well. I'll also compare the L5 to the L6, which I got awhile ago. . . I can't tell any difference betweent the output or beam quality of the L6 compared to the L5. The L5's compact size (compared to the L6) would make it my first choice among these two Surefires for this reason. But cost makes it a tougher choice when compared with the T3.
If beam quality is paramount and cost is no object, get the L5 (if you can. . . I waited months for mine!). Otherwise, I think you'll be happy with the T3. Or do the CPF thing. . . get 'em both, then you'll be sure to be happy!