Versus Toughness 3 (applying rerolls to “To Hit”*):

Wolf Claw: 4 Hits, with 1.3333 additional hits after rerolls. So, you have 5.333 total hits, which result in 4.444 “wounds” on average.
Frost Blade: 4 hits, 3.333 wounds.
Result: Wolf Claw wins by 1.111 wounds.

*Please note this is the ONLY circumstance in this model where you should apply your rerolls to hit instead of to wound. The reasoning is simple: It’s better to reroll 1/3 of something than 1/6 of something, right? Right.

Versus Toughness 4 (rerolls to wound):

Wolf Claw: 4 hits, 2.666 wounds, .8889 with the reroll, 3.555 total.
Frost Blade: 4 hits, 3.333 wounds.
Result: Wolf Claw wins by .222 wounds.

Versus Toughness 5 (rerolls to wound):

Wolf Claw: 4 hits, 2 wounds, 1 more with a reroll, 3 total wounds.
Frost Blade: 4 hits, 2.666 wounds.
Result: Wolf Claw wins by .3333 wounds.

Versus Toughness 6 (rerolls to wound):

Wolf Claw: 4 hits, 1.333 wounds, .889 more with a reroll, 2.222 total wounds.
Frost Blade: 4 hits, 2 wounds.
Result: Wolf Claw wins by .222 wounds.

Versus Toughness 7 (rerolls to wound):

Wolf Claw: 4 hits, .667 wounds, .556 more with a reroll. 1.222 total wounds.
Frost Blade: 4 hits, 1.333 wounds.
Result: Frost Blade wins by .111 wounds.

Versus Toughness 8 (rerolls to wound):

Wolf Claw: 4 hits, .667 wounds, .556 with a reroll, 1.222 total wounds.
Frost Blade: 4 hits, .667 wounds.
Result: Wolf Claw wins by. .667 wounds.

Conclusions:

The results seem pretty clear. There is only one scenario in which the Frost Blade comes out on top, and that is versus Toughness 7 targets (because there are lot of those flying around!) In every other case, the Claw is the clear winner, coming out furthest ahead against Toughness 3 targets where it can make best use of it’s “selectable reroll.”

Now, the Frost Blade has a few other bonuses which I should mention for the sake of full disclosure, which is that it IS strength 6 for purposes of penetrating armor, and it will cause instant-death on Toughness 3 models. If that is enough of a bonus for you to pay 5 more points and lose some effectiveness in other areas, then go for it.

But being armed with the facts makes for better decision making in most cases than “Hurr!! I’m Strength 6… OWNZORS!”

"It’s possible that the player could use a Belt of Russ and get the off-hand attack for the Frost Blade, and in that case the Blade would probably come out slightly ahead in the calculation. You could get the same effect from a second Wolf Claw, but you would end up spending 15 more points for it. If you REALLY want to eek out that one extra attack, the Frost Blade is probably a better buy. "

Assault
FW - 12.48 attacks = 6.93 Wounds
WC - 11.06 attacks = 6.55 Wounds.