Homebrew damage spells

[MichielHagen]

I want players to be able to create their own spells, how would you compare the following spells to each other:

All are same type of damage, SR applies.
5d6 ranged touch, range 40 ft
5d6 cone, 15 ft, reflex half
5d6 burst from self, 15ft, reflex half
5d6 line, 30 ft, reflex half
5d6 radius spread 5ft, range 40 ft, reflex half

Does one seem much stronger or weaker than the other?

Personally i think the radius spread is strongest.

Also, if i take the radius spread as example, if i upgrade it to 10ft radius spread, the area becomes 3 times as large. Obviously the "cost" should not triple as well, since it is unlikely the amount of targets hit also triples. Would multiplying the cost (lets say feats) with 1.5 seem fair?
In other words:
Would you prefer a
6d6 radius spread 5ft
or
4d6 radius spread 10ft

I think i would go for the 6d6....

[Kamai]

I want players to be able to create their own spells, how would you compare the following spells to each other:

I would probably put them in this order:
5d6 radius spread 5ft, range 40 ft, reflex half
5d6 ranged touch, range 40 ft
5d6 line, 30 ft, reflex half
5d6 cone, 15 ft, reflex half
5d6 burst from self, 15ft, reflex half

I agree with you that the radius spread is the strongest, and on a Wizard/Sorcerer chassis, the burst is much worse than anything else here. Self-centered bursts need a lot larger payoff due to creating a zone around you where you cannot have allies. Ironically, because of this, increasing the radius of a burst is as likely to be a determent as a benefit.

Also, if i take the radius spread as example, if i upgrade it to 10ft radius spread, the area becomes 3 times as large. Obviously the "cost" should not triple as well, since it is unlikely the amount of targets hit also triples. Would multiplying the cost (lets say feats) with 1.5 seem fair?
In other words:
Would you prefer a
6d6 radius spread 5ft
or c
4d6 radius spread 10ft

I think i would go for the 6d6....

If these are the only 2 blasting spells at that level? I'd feel just about right taking either spell. However, if there's a spell balanced for a truly single target blast, I'd never take the 5ft radius spell, because I don't feel like I could rely on it hitting multiple targets.