I found a guy an eBay called ROBSSTRINGSHACK who lets you order custom packs of 6 guitar picks in most of the popular Dunlop lines. I've had an absolute blast the last two weeks having dozens of picks in different sizes and makes lined up across my desk and shredding a few minutes with each to compare them.
I've used Tortex and Gator Grips for years because the marketing convinced me that plain smooth Delrin picks would slip out of my grip. Well they don't, and the plain Delrin have ended up being one of my favorites as far as tone and feel. They have such a crisp, smooth release and bright tone when shredding.
I found that my least favorite has been the regular Jazz III. It sounds like a cheap piece of plastic and the front edge is almost too sharp and feels like it gets stuck on the string. The same Jazz III made from Ultex is one of my favorites. It is sharper than a normal pick which gives you more precision and a snappier release, but is much slicker than the regular Jazz III and does not have that plastic sounding plink to it. Another that I do not like the sound of is the Ultex Sharp. The regular Ultex is one of my favorites, very slick and fast, but the Sharp version has a pronounced "ping" to it that I find annoying. If it were a lot thicker, I think it would help. I wish Dunlop made the regular Ultex in a thicker 1.5 and 2.0.
The Gator Grip picks feel like they take longer to get over the string and have a more muffled darker tone. I like this for some applications as well. I'm liking these when I am learning a new pattern. The Gators feel like they are slowing your shredding down a little while the regular and Jazz III made from Ultex and the Delrins have a very slick, dry, quick release. The tips are a little more rounded on the Gators too, so they roll over the string more smoothly and feel like they stay in contact with the string longer.
The regular Tortex versions are good all-round picks, not too slow, not too fast, and have a balanced sound to them whereas the Delrin is brighter and Gators are darker. I have some more on the way, and will add these into the mix. It has been a lot of fun and certainly costs less than trying new pickups.
As far as pick SIZE, I haven't found anything thinner than .73 useful for anything but strumming chords. The .73 picks are on the verge of being too thin for the shred, blues, rock, and metal I play. I have found the 1.0 and 1.14 to be a good all-round balance for everything. The 1.5 and 2.0 begin getting really thick and feel like they take longer to get over the string than the 1.0 and 1.14. This is useful for some applications, but I no longer agree that the thickest pick you can find is best for shred. The composition of the plastic and the shape seems to effect the speed of it more than the size.