Well, simple physics says a more massive bow takes more work to accelerate than a lighter one. When playing really fast stuff you use just your wrist (or even just fingers), so a heavier bow is going to be more work. But a "heavy" bow might be 62 grams and a "light" one 58. A gram is not much, and even 4 of them aren't much. Your fingers alone might be able to detect it, but the difference in how long you could play before they gave out wouldn't be large.

Probably a bigger factor is the balance point of the bow. That will make it seem heavier. A bow (A) with the balance point nearer the frog than a second bow (B) will seem lighter to the hand, and will actually be lighter at the tip (where you tend to do a lot of this style of playing).  Unfortunately, bows are not usually described with their balance point. (And there are some issues as to how that ought to be measured so that you could legitimately compare bow A to bow B.)

There is no such thing as a bow that is perfect for Irish/Celtic music. Even if there were, it would probably have to get that way by being very poor at other things.

My advice would be to avoid heavy bows and "soft" bows (whatever the opposite of stiff is), but otherwise try as many as possible out, playing the type of music you want it for, and see what works best.