Please VOTE for your favorite Christmas Project selection.
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.
About the weight, I was thinking about when the bow is in motion. Then it has to be stopped and reversed in direction VERY abruptly and usually repeatedly. When you consider this is done mainly with the small muscles of the wrist, not the stronger ones in the arm, I just thought that small difference might be somewhat significant. Maybe we don't even consciously feel it.
@Fiddlerman Thanks! I took the pictures with my iPhone and had trouble keeping the phone from shaking. One of the drawbacks of nerve damage. I will file that info for after I get the other bow re-haired. Thinking that when I am done I am going to sell the Brazilwood bow since I find it so hard to play with. What is the point of hanging onto something you will never use!
"Reality is an illusion, albeit a persistent one".- Albert Einstein