i use 1.14 pick, and i found it is better than soft pick.for me pick does matter! i just learned sweep picking for 3 months something, last time was horrible, but now the sound of my sweep is not so clean. but i think the problem is yer hand position while sweeping upward. yngwie's hand position maybe not suitable for you! and i think you should try and error, and you will find the best way of sweeping hand position that suit you. (i am doing like that... hope can help you)