I myself never play sinx (sin so far) and I want to be smart ass a bit. Bear with me :p
On moscovia dungeon 3, there is monster similar (loots value) to succubus, incubus -> mavka. I think fire damascus + any DD dagger is good enough.(ignore other monsters). Consider the steal chance too when you are going to kill monsters on any place.
The raw attack difference between +4 and +7 ice pick is 21 + 1 ~ 42 attack, calculated before defense piercing goes in.
+4 and +10 would be double of that....
+4 is good enough if you want to spend zeny on other equipments, mostly you want your first ice pick because of the effect not the upgrade.
ignore DDP and DDTP they only give slightly difference, usually people go main hand DDP glad + right hand ice pick if they have <=120 - 130 str, otherwise DDTP.
The more important thing when you are mvp-ing, do you have the right element? (ex: ice pick + any DD dagger + aspersio for LoD)
Just for fun: you can one-shot soul breaker succubus + incubus, using holy weapon + ice pick.
I never try rideword hat. But it's definitely good for sg, you might consider that. (p.s. ask someone who already use it for a while)