Yes, I had a Daystar 2 1/2 X 1 1/2 leveling kit.
I actually went with the Toytec Superflex rcc2.0HD. I don't recall spring rates, but they're posted in the suspension sticky. However, the OME 895 is supposed to be 40% stiffer, the Toytec sfrcc2.0hd 25% (1/2" taller too), and the Toytec sfrcc2.0 10% stiffer than the stock springs. The feedback from many is that the OME 895 were very stiff (almost harsh) when running empty. I don't have any extra weight in the back (after market bumper, tools, etc...) and I run empty quite often. However, I do carry people and sports gear (skiing, biking, hiking, camping) often along will towing a PUP from time to time. I thought going with the spring stiffness in the middle would be the best choice for my use of T4r. So far I love the ride and alignment ended up pretty good too (castor was in spec with Daystar and not with OME). This is not my DD so it will take a little while before I get some good time behind the wheel to share final thoughts on ride.
I can't comment on MPG change as it was already lifted. However, I'm typically getting 16-18 even with my Yakima rack up top, including trips up I-70 westbound! Not bad at all for a lifted runner with a V-8!!!!