In doing some checking it is very hard to find Power Pro in white, it is also quiet a bit more expensive than silk. I checked and it is made from polyethylene and is kind of like kevlar, they brag about its cut resistance and even use it in protective wear. I have a spool of it, moss green 20 lb test, I have not used it yet for pearls. My problem is the sharp feel of it. If you take two strands and knot it and pull it tight and then run your fingers over it, it feels very sharp and rough. I would think this would be worse than a bead spacer on the pearl. Also checked a few of the large retail sights and one even mentions only using pure silk to string pearls under their care guide.
Darla
I will try to summarize some of the threads already up on silk vs synthetics so this will be a long post.
There are already several threads about this
Try this one. 2-3 years ago we had a little challenge on silk compared to power-pro. I made a bracelet of pearlluner pearls and power- pro and wore it 24/7 including showers, dishes, sweat, for over a year. It came through really wonderfully. It did not wear the pearls at all. The silk challenger gave up the experiment and faded away. So far, no one has reported any wearing of the pearls from it. I haven't seen it in mine at all.
To take it apart is hard. Very few to no scissors can cut it, but thread clippers do a great job. When they wear out, they could be sharpened, but they are so inexpensive that I buy 4-5 at a time.
There are some caveats to Powerpro, the lack of colors, the roughness, difficulty of cutting it. There are some pros. It is the strongest thread available, it is prewaxed. The knots slip into place easily and stay in place once tightened. They are easy to move longer distances. I moved a knot over a foot to get it seated once and had no problems. Try that with silk with no tool to keep it from clenching. It is much harder to make a ruinous tangle and most tangles come out easily. I can't tell you how many times I had to start over because silk has tangled on me. I know how to handle silk and always prewax it.
I have used PP exclusively since I found it. I have work-hardened hands and the roughness doesn't bother me at all. There is no better thread for a heavy piece. I made a 30" necklace of 16mm cfwp's and it stretched in 5 minutes of wearing. That sent me on a search for a thread that would not stretch resulting in me finding Suzanne Hye on eBay. (Suzanne learned to knot directly from Harriet- harriet is the one with the classic how to knot book.)Suzanne is also the one with 54 spools of gudebrod silk for sale right now. I just gave her link above.
I have no objections to the silk thread lovers. It was only when silk was not easy to find I suggested synthetic threads. All my statements in this thread are made after using PP for years with no problems. One of my criteria is "hard to break", which silk is not. another is "no stretching, which silk is. Another is to be fully washable without stretching. Another is "no rotting" It is simply the best for a heavy necklace or an endless necklace. The knots stay put. I had one incident where a pearl with a sharp edge cut the thread. I reamed it a little and believe it has held up since.
I like griffin nylon for its colors and it does hold up longer than silk. I want to try gudebrod synthetic. I am sure is is a fine product. Beadalon dandyline is also made from a spectra type product. It comes in white and charcoal gray. It is easy on the hands, very silky feel. I started a thread some time ago which covered a lot of threads, including linen, hemp and a few others. I have been trying threads of every kind since I fisrt started beading more than four decades ago. I have used monofiliment thread, sinew, you name it- I am always willing to try a new thread. PP turned out to be fantastic for peyote stitch- you sure don't want that thread to break! I also used to do bead embroidery on leather. If I ever do it again, I will use PP. It simply meets my needs, except for color.
PS, I am moving this thread to the Lowly Beaders club which covers all things thread.
Did anyone check with Bellafindings? They always call me if a product I order is out of stock (findings) and ask if I would like to pick something else, prior to shipping my package. Francis is a great guy who almost always make those calls (sometimes another lady makes the call) or handles exchanges and returns phone calls. 
