I purchased the 5/8's blade, and I hate it, hard to get it to cut hair. I use the heck out of my medium blades. I have used about all the ones they make, and my favorite by far is the new one Called X-blend from sullivans. I have actually clipped a few heads with my blending blades in a pinch and it actually looks better then using the #10's. I also love my opti block and Xblock blades.
What do you use the T-84 blades for? I have one, but only use it when ALL the others are dull, havent quite found its purpose yet.