@Shran No. According to the book 100% as RAW:
“Results of 5 or 6 are referred to as Effects. Specially-made Conan Combat Dice replace the
1 and 2 sides with success icons, and the Phoenix icon for the 5 and 6 faces, with the 3 and 4 faces left blank. An Effect adds 1 to the total, and also triggers certain abilities, such as weapon Qualities and other special conditions.” - Page 93.
IE the effect gives 1 damage not the die is 1 damage and it causes the effect. You are referring to the table which is strictly showing how much damage is done, simply writing effect there would be confusing. The rules are crystal clear in the text though. 5 or 6 = an effect. an effect = 1 damage+triggering effects.
So @Valyar is IMHO correct. All dice become an effect. If it had Vicious and you rolled 4cd you end up with 2 points of damage per die and 8 total damage.
@Stokar But you never have to choose to spend till after you roll. On a roll of 1,5,5,2 you already do 7 damage. Spending 2 points of momentum is a waste. There is no reason to NOT roll.