Before you decide to tank, check if you actually can make it. If i decided to tank right now in my 35T, most likely i wouldn't make it. 8th place has 22 points in 15 matches, i have 41, so he'd have to make 20 points on 13 games, an higher number of points per game than he got so far. At least it would be very very close, and risking to get promoted, without qualifying for CL would only make matters worse.