I cant talk about 7, but I took 8, and then I took 4...and 4 was beastly hard, compared to 8, especially the verbal...
but i think the general rule of thumb at SDN is that 8, 9, 10 are more like the real exam. You proally will get steady scores no matter which test you take, cuz thats how the test is engineered (the curve is built in). But, the material covered, the way it's asked, and how many you get right are more correctly represented in 8, 9, 10.
Thats how i think of it...but once again, scores dont matter at this point...just get as much practice as possible. only one score matters and lets hope it boosts our ego X 10. 🙄