I believe Feanor has less power than Deathwreaker (but dont quote me on that); 12 speed and 12 stealth should be more valuable than what Feanor has, no ?
Last version I recall they had 15 speed and featherfall or somesuch.
I know of no reason why Feanor boots couldnt get rolled as boots; I assume they can (and become 8 speed 8 stat in the process or so).

Feanor has +15 speed, resistance to nexus, and activation for Haste Self. That activation is pretty powerful, especially since the recharge time isn't that unreasonable (200 turns).

That said, it's usually just an extra +5 speed over what you'd be wearing otherwise, which is great, but not the kind of game-changer that Deathwreaker is.

Deathwreaker used to be too heavy to get full blows with it. It also aggravates, so it isn't that useful, and it also isn't that big game changer unless you manage to get it early. MoD of Extra Attacks +2 can be very close to be as good as D is, or if you get lucky with bonuses even better if you play mage or priest (50% more blows).

That +5 to speed from body gear is actually quite big deal. It is usually enough to tip the scale to make new choices for rest of your gear. That is one of the reasons why +3 from Thalkettoth and +3 or +2 from few of the artifact cloaks and Trickery amulet also are big deals. They stack up freeing up a ring slot, and that is why even small speed boosts outside rings are big deal.

I wonder what the blows formula used to be; "too heavy for full blows" these days translates to "only the warrior wont get his last blow, everyone else is fine even without maxed str/dex".

Notice anything these have in common?

(and, yes, these are all in the same game... which I'm re-playing right now. I just have to see how powerful this will make a Priest. Of course even if I find both rings, one of them will probably have to be swapped with a speed ring.)

Been there done that :P

Its fun, and none of these are based on a super-rare like Feanor. This is when other artifacts with ~10 speed become interesting; body-armour or shield.

Also, is there a good weapon that beats a MoD of slay evil ? (with 6 off-weapon attacks, another +2 from weapon isnt best option, rather take the slay).

Not sure about the weapons -- there isn't anything that stands out particularly, but there a few weapons with big +to-dam.

Holy Avenger MoD would be good, plus it's possible your randart set has an item with "causes your attacks to slay XYZ" or "brands your melee attacks with XYZ," which would be worth stacking with your extra blows.

Random thought that I don't know where to put: Maybe instead of the power of a randart being how much stuff is on it, it should be how much BETTER it is than the typical ego you would have put in that slot otherwise (so for example artifact boots with +10 speed will have a very low power level, due to +10 boots of speed, but artifact hat with +10 speed would be comparatively very valuable)

Do you mean before fractional blows? Or even earlier? It used to be that some of the five-blow classes did get only four out of them. IIRC Rogue and priests didn't get five with it (now priests get four anyways, so that's "fixed").

With fractional blows IIRC even warrior gets max blows with MoD. Unless that has been revised somewhat DEX affect to blow calcs doesn't stop in 18/150 like it used to be.