1. I wouldn't worry too much about the floaties in the SN. Could be hops, could be other "stuff" settling out of the beer. I can't say with 100% certainy what the "stuff" is . . . I'm not an expert on the "stuff" (coagulated proteins I think?) . . . but I've seen it in my brews and had no probs. Just wait until it all settles out in your secondary befor you bottle.
2. The size of the carboy shouldn't matter too much unless the krausen when you did it in the 5 was right up by the neck, which would form concentrate it all in one place. Yeast strain may make a difference, but my guess would be that it has more to do with timing than anything else. Temp differences from when you pitched, viability of the yeast when you pitched, other factors could change the timing on when you'd see a high krausen vs. a low krausen. Don't worry about it.