Hi;
I can offer my experiences with the r8 in that I have had two of them.  The r8 is four or five feet taller than the r7.  The swr for whatever that is worth, is significantly better on 40 with the r8 than the r7.  The r7 is rated at about 75 kc under 2/1.  They aren't kidding it goes up rather quickly after that.  The fact that it is a shorter antenna, however, makes it much more durable in my opinion.
The r8 works much better on 40 and doesn't make the tuner work quite as hard.  When mine was assembled everything worked using factory settings except 40.  You had to raise and lower it a few times to get 40 to be in the ballpark.  I found that the antenna bent or snapped near the base when exposed to high wind.  The company recommends at least three guithe ropes.  Don't buy their guithe kit.  It basically consists of ho hum rope and three large stakes to drive in the ground to attach the ropes.  Depending upon where you are installing it, you might just attach the ropes to the roof and the rather expensive stakes get recycled.
Richard