If I were to,
{Counterlash} an Instant spell, can I cast an Overloaded {Cyclonic Rift} for free?
Or is it the cards main cmc?
When casting a card with overload for free, you are only able to get its original effect. This is because "overload" and "you may cast x card without paying its mana cost" are both considered alternate costs, and you can only apply one alternate cost to a card.
Also, I believe this should be under "Rules".
RESOLVED
I cannot give you more karma today, thanks!
This would fit better in the Rules section.