Damage-wise, yes, Greyswandir is the best weapon, but other weapons have useful properties. Not that I would consider using anything other than a bladed weapon on a samurai. Can samurai reach expert in sabers or are they stuck as skilled or basic? Also, can they twoweapon at skilled or was that at basic? I'd look it up but I don't care. If sabers can't get up to skilled, twoweapon long swords. Frost brand+katana is very competitive with Grey+silver saber. If samurai just plain can't twoweapon well, then get a GDSM with the hope of getting a shield of reflection later. If this is all confusing, just get Frost Brand and #twoweapon with that katana you have.
Wish one should be 2 blessed ?oCharging (if you already have ?oCharging ID'd, wish for a blessed magic marker and write a new blessed ?oCharging). Wish two should be SDSM or GDSM (I'd probably pick the SDSM because other cloaks kind of suck, but it's your call). Wish three can be your weapon of choice, be it Frost Brand or Greyswandir. Wish four would be speed boots. Wish five can go ahead and be two amulets of life saving, although I'd consider a quest artifact if I could survive the blasting. No advice there since I can't remember any of the lawful ones.
Tip of the day, use wishes until the wand runs out of charges, then charge it with a BLESSED scroll. Zap it some more until it runs out again, then keep zapping it until you wrest one last charge out of it. You can get upwards of 7 wishes this way if you get really, really lucky. You're more likely to get around 4 or 5, but you're guaranteed at least 3 if you recharge and wrest that last charge out.
Another tip, always wish for "blessed fixed greased" versions of what you want.Also, if the item can be enchanted, wish for it to be +2 or +3. If it can't be enchanted, wish for 2 or 3 of the item. If you pick 3, be aware that the item then has an increased chance of arriving unenchanted or alone than if you picked 2. For example, if you want +2 gray dragon scale mail, you'd wish for "blessed fixed greased +2 gray dragon scale mail". Fixed just means corrosion-proof while greased means covered in grease. The grease probably won't matter and many things can't be corroded anyways, but it never hurts.