I picked up 70/30's and drag shocks but I was already spending like $550. Then a wave of common sense hit me, I searched for Tokico 5-way adjustables and got them for around $450 shipped to my door tax and shipping included off ebay( I returned the drag suspension). We put them on and it is a night and day difference. Let me put it this way - I haven't even adjusted it to the "drag" or "loose" settings yet because I love how they respond on the tight setting - yeah apparently I had stock struts and shocks in my car - these were a MAJOR upgrade! I took a right hand 90 degree turn going 30 and threw the car sideways and it gripped so hard that I almost overcompensated for the roll like my "old" suspension previously handled - I suggest going adjustable, its cheaper, more versatile and will relatively accomplish the same goals as the ALL drag setup.
If you go ALL drag like you stated, then go ahead and pick up a set of 4 cylinder springs from a mustang junk yard and install them on your car - that will save you a couple hundred bucks and has the exact same effect of drag springs too.
Good Luck