(Vaal) Spark vs (Vaal) Arc totems

Greetings,

I have been working on an Arc totems build, converting damage to cold with rings, which has worked really well so far. Well into T16 maps, but I am confused.

The sheet damage for the skills says 20k dps, with buffs, I get it to 40k.

I am using level 20 quality 23 Arc gem.

If I switch out to level 19 quality 23 Spark gem the unbugged sheet damage goes up to 44k.

Spark does not appear to clear as quickly as Arc does though.

I don't use flasks or anything like that to get extra special damage (consistently) either.

I have 4 power charges and a lot of crit.

Is Spark (supposed to be) that much better?

I am doing okay with the build, but my Frost Totems templar has a much faster clear speed. Not sure why yet.

Thanks for any tips or advice.

Cerni