zpacks Arc Blast vs Blast? New packs?

Yes, mine has the roll top. To me there isn't really much difference. The roll top has a velcro like closure then you roll it down. With a draw cord (like on my GoLite Jam) I roll it down after closing as well so either way to me the concept of rolling down any excess makes sense and works well.

Having said all of that I probably prefer the draw cord just because there is a little less fiddle factor (i.e.,you just grab the cord and pull and then roll down excess whereas the Arc Blast you line up the edges and press together and then roll down.

I talked to Joe at ZPacks and am ordering Cuben seam tape and going to tape mine myself. He said it should take about 6 of the strips he sells and that you just need to put the bag inside out after removing the frame. (or you can ship it back and they will do it for a small fee)

I've had one minor stitch already go on the shoulder strap (my fault for swinging the bag improperly instead of using the haul loop). So reinforcing the stitching as well as waterproofing is worth it to me. It adds an ounce, but then if i can leave my pack liner behind, I save an ounce, to make it a wash except that my bag is now easier to pack.