Tried these two sleeping pads in my Ridgerunner this afternoon. [Looked for the Klymit Inertia XL, but couldn't find one around here, and was hoping for more insulation than that seems to have.] I can't stand the crinkly sound some pads make, so didn't give those a second look. The Sea to Summit has a similar size as the Klymit, which at first I thought would be too long, and has a similar overall shape as the shorter ExPed.
Here are my comments on how the ExPed and Sea to Summit compare as a pad for the Ridgerunner hammock.
ExPed's SynMat Hyperlite (M Wide: 25.6" x 72") is orange on top and charcoal on the bottom. The fabric feels durable, and slightly fuzzy. This MWide size was a little too short; because it narrows at the foot end, my feet tended to fall off the pad on one side or the other. I didn't realize that at first; their Long Wide version (L Wide: 25.5" x 77.6") would have been a better comparison. The longitudinal tube design means this pad doesn't fight the hammock's curl, cradling me. I felt higher on it, so a bit more tippy. But, when mostly deflated, I felt my butt bottom out and get cold. ExPed has a clever flat valve that makes inflating easy, but deflation exasperating (at least, to me). The ExPed has an R rating of 3.3, and this model weighs 14.6 oz (their L Wide weighs 15.7 oz).
Sea to Summit's light green Comfort Light Insulated pad (Large: 25" x 79") is a newer design, out this year (Backpacker liked a fancier variant; Outdoor Gear will review this model in August). It needs less air to fill than the ExPed; I felt a little bit lower but still well cushioned. Lots of little tufts of cushioning; when mostly deflated, I didn't bottom out. It has a two part flat valve that makes either inflation or deflation easy and fast, so not only does it fill faster, it was easier to deflate and get back into its stuff sack quickly. Because the Sea to Summit is longer, it felt wider than the ExPed around my torso (and feet); not sure if I would say that of ExPed's L Wide version. This pad sticks out of the RR's double layers about an inch on each end. When manhandling it into the hammock, it gave me shocks from static electricity that I did not get from the ExPed. Sea to Summit claims an R rating of 4.2 for this model, and it weighs 24.5 oz.
After trying both (briefly!), decided the Sea to Summit fits my Ridgerunner better. If you are concerned about weight, the largest ExPed would be a decent choice. I've heard good things about the Klymit, as a light summer (only) pad, as well.
Hope this information is useful to somebody.