Why not just change it to:
1 HD + 1 HD / 1 level, up to a max of 10HD
Full round casting time
Will saving throw neg
Target: 1 or more creatures no more than 10 ft apart
Given as a suggestion only. If the 3.0e version is too powerful, and the 3.5e version is too weak, make it work where it still is useful at higher levels, can't take out a whole group easily at once, but it is still a threat.
Let's face it, a standard group of 1st levels can watch their sorcerer or wizard die from a 3rd level caster using magic missile and a 3rd level caster could be a difficult but not overpowering challenge to a group of 4 1st level PC’s. So what if a spell is dangerous at low levels, so is a house cat or a great sword swung by the never ending fighter. No one ever said adventuring was easy or safe.
I have a problem with the fact a wizard or sorcerer can throw off their one maybe 2 first level spells at first level and be done for the day except for 0 level spells which amount to nothing, and then risk the one hit kill in melee combat. Whereas the fighter types can swing his weapon (no matter the choice large or small) once per round every round all day long without any penalty or problem in game until he runs out of hit points like anyone for that matter. Add to that the rogue and clerics can do the same can be protected by armor but the poor arcane spell casters better jump at the slightest thing cause they are done and can't do anything after casting 2-3 little spells of which the spells have been nerfed to "protect them at low levels" load of bull.
I don't favor the spell casters IMC, but it does seem a bit unbalanced to me. Granted a spell caster that makes it higher level can do some amazing things with the spells, but then they run out and fall back to that one good hit and their toast mode due to low hit points and no armor. Whereas the high level fighter types just keep on going swinging more and more and doing some amazing amounts of damage round after round after round.
Sorry for the rant, but the nerfing of spells and spell casting is one reason my group and I are still using 3.0e primarily with few things borrowed from the SRD for 3.5.
RD