I was wondering if you can provide a list of past theologians/preachers who you believe significantly entered the realm of Mysticism/Pietism to the detriment of themselves and their fellow believers.
I believe you would name Pink, Murray, Philpot, Gill on the list....anybody else significant? What about Edwards? Darby? I know there are no perfect preachers but I'd like your input on those you feel have crossed the line....
I really don't think it would be beneficial to provide a list of Mystics.

From the few you listed, only Andrew Murray and J.C. Philpot would make my own personal list. I'm not well enough acquainted with Darby to say he would fall into the "Mystic" category. However, he was certainly guilty of serious heresy with his Dispensationalism. And I will also say that Jonathan Edwards was no Mystic.

Plus, could you be as specific as possible on how you would draw the line between true experiential faith/preaching & Reformed mysticism/Pietism?
Again, I do not think it would be profitable to provide a definitive line between true experimental preaching and mysticism/Pietism. Generally speaking, my personal observation has been that those who setup some emotional/experiential standard that all should strive for or even worse, a standard by which one is to be judged as being saved or not are to be avoided. What I believe Scripture demands is faith, repentance and a striving after holiness. We all fall woefully short in all three of these, but the Spirit within motivates us to do so for all our earthly days. Our eyes should always be upon Jesus, the Author and Finisher of our faith and not some arbitrary experience determined by some man. Most of the Puritans had the proper focus. But there have always been a few who have been enamored with Medieval Mysticism, a "deeper life", a distorted and unbiblical standard by which one is to conform. If Paul judged himself to be the "chief of sinners", how much more am I to judge myself before God?

Salvation is by GRACE alone, through FAITH alone, in CHRIST alone.
also, who would you recommend as having a balanced view on these matters? Spurgeon, Owen, Bunyan...Beeke?
Yes to all of the above. And, as I mentioned already,
most of the Puritans had that balance for the most part.