Just want to mention how it's working for me: I will be placing a lot of accuracy in my relic (121 points all in all) and then meld the rest into my left pieces, except the boots.
Because with relic + melds + buff-food I will hit exactly 600 Acc. I will meld Crit and Spellspeed in the rest of the pieces ^^ (Spellspeed in those where crit is already capped.)

As far as I discoverd it's not necessary to meld any VIT, except you are really really undergeared!