Luck 1 means, that you (as a bg for example) suffer for bypasses. But still, max hp 1lk char is pretty decent.There are few SPECIAL points left for BGs, so maybe someone should try 2 or 3 lk build, and check the difference (or maybe done it and be so kind to tell us the results).
On paper, 5 LK vs 10 LK is just a 5% difference in critical chance. Not much, and costs a lot of points which could be used for PE or EN.
The second being maybe for BG builds or something like that but what about perks like right between the eyes and spray and pray?
Depends if you aim in body parts.
Tested it makes no difference. Best to just take anti-cripple, anti-knock down perks.