I don't know how they compare in size to Rhino, but I have both the Northwind Turnout Sheet and the mid-weight Turnout Blanket and I really love them. My horse is hard on his clothing and has not been able to rip either one. My experience with the sizing is that they are true to size in a nice generous sort of way (if that makes any sense!).
I love the Northwind blankets and Dover holds true on the 2 year guarantee. I had a Rhino sheet and comparing that one to the Northwind's, I would say order a size up in the Northwinds, especially if your horse isn't the narrower TB type. My horse measured a 78, and while the 78 Northwinds fit him, his butt hangs out a bit. The 80 fits him better - he's an Appendix and he has a big butt ;-)
up the hill from the little river (that floods alarmingly often)
My TB/QH mare takes a 75 Rhino/Rambo and a 74 Dover Northwind. Her 75 Rambo is a bit big, but her 75 Rhino fits her pretty well. Her 74 DN sheet fits very well, though the tail flap on those is shorter than on the Horseware turnouts.
I love the DN sheet—it fits well, it doesn't move, it's held up wonderfully and I love the reflective piping.
Mine is on its second season. Last year when I got it back from the cleaners it looked brand spankin' new!
Smith Brothers has the same blanket (listed as their two tone turnout) for alot cheaper - it even has the Dover Saddlery logo sewn on the front! I ordered mine from there instead and I really like it. It is the heavy weight though.
This is the one I got. It's normally 109.99 and that's what it comes up as in the catalog, but if you search "smith brothers two tone turn out" you can find it for this price. I have a Dover turnout sheet and the smith brothers fits just the same