300 ppi in photoshop by itself means nothing. Did you scale the image? What's the Effective PPI when you check the Info?
Even an effective PPI of 300 may not be enough for sharp edges. I typically like to see 1200 or more for line art going to press.
I actually just ended up doing my effects in InDesign and acheived a similar look. Thank you very much for your reply, I will keep it in mind for next time.