We know Arthur and Lancelot have them, and I think Gawaine has a sword named Ghalatine. What other people have tyhem? what are these items supposed to do? and.... How can the uses be transferred to game rules? I have some of my own ideas but I want yours. ;D

In my game, I use the +5 and no armor NOR SHIELD. Arthur's Sword is hot, but Excalibur need not be the "Ultimate fighting weapon"... it merely needs to be very good. So against any Skill 25+ character, Excalibur SHOULD be fairly unimpressive; normal knights are 12-18 skill with sword. A +5, especially if Arthur Inspires, as well, is a powerful enough weapon for the non-over-the-top normals of the knightly class.

And note: Inspiration is +10 in 4th ed...
... And Arthur is usually able to inspire. Loyalty Vassals 26! At least in 531

So Arthur can expect to be going into a duel with a Sword at 20, +10 for inspiration, maybe even +20 from a crit Inspire... and a +5 sword. Against mere mortals, effective sword 35 is brutal; adding no defending armor means Arthur is critting 3/4 of the time, and thus doing 12d6 vs Chivalry+HP.... Excalibur thus is a cleaving blade in Arthur's hands... Do NOT face Arthur when you've inspired him.

And even then, if he doesn't inspire (or has inspired on battle, his normal), he's still Skill 25, possibly +5 for charging, and doing 6 or 12 dice against no armor... it really is a POWERFUL weapon that way. Joe Normal Knight, taking 6d, is taking an average of 21 points no armor, and 1/4 to 1/2 the time, 42! Instant major wound, if not kill. Any hit matters a LOT with Arthur's 6D damage and no armor.

It is, mathematically, not quite as nice as a +10 weapon, putting inspired arthur at Sword 40, and uninspired at 30... he can expect to do a crit, but uninspired, half his hits are 21 pointers, reduced by 12 most of the time, for 9 point hits, and by 18 if they got shield (doing average 3!), impressive; not deadly; the average crit is 42 points, reduced by 12, to 30; kills young knights, and puts most instantly out of action.

I'll probably go with +5 and ignores armor and shield. It fits the literature better.