Your Fighting and M&F skill levels are also relevant since they multiply base damage. I'll assume you have about 16 in each and thus get about +60% to base damage. The STR you have mentioned also provides you about +37.5% to base damage. These stack multiplicatively, to become +120% base damage.
So a demon whip's base damage of 11 becomes 24.2, and the eveningstar's base damage of 15 becomes 33.
As Siegurt mentioned, slaying and AC are going to affect the demon whip somewhat more because of its lower damage. To make things simple, let's assume slaying cancels out enemy AC (which, assuming you have no slaying sources besides enchantment, is going to be roughly true on caustic shrikes and liches).
The demon whip gets 7 attacks per the eveningstar's 5, so with our assumption that AC has been canceled, we can just multiply 24.2 * 7/5 = 33.88.
So with these assumptions, before factoring in brands, they are doing pretty much the same amount of damage, with a very slight edge to the demon whip.
This is looking like...exactly what Siegurt said. Nice. So yeah just read his reply. I would just add that most enemies are susceptible to electrocution, while very few are susceptible to holy wrath, so you should probably use the demon whip.
Siegurt wrote:Note also that slaying will push the damage more towards a dWhip advantage, but it would take a whole lot of slaying to push it's damage past the eveningstar's damage against holy-vulnerable critters.
This is purely academic, but, I don't think it's possible for the demon whip to surpass the eveningstar when the holy wrath brand is activating. While the demon whip naturally applies slaying more because of its speed (7/5), the eveningstar will apply slaying more when its brand kicks in (1.75). Both increased speed and holy brand can be considered post-AC modifications to damage and in this case holy wrath is the greater multiplier.