First, you published a number without a reference. Secondly, if it's a published 70-90 MPH spec, then it's a top gear roll-on without downshifting first. There's no way the E90 takes 3.1 seconds to go from 70-90 in the optimal gear.
Thirdly, you quoted a the P85D's 70-90 as 2.5 seconds. You probably got that from here:
0-60/30-50/50-70 comparitive times for 70D/85D/P85D - Page 6
Which also quotes the P85D's 50-70 at 1.65 seconds yet the fastest I've ever seen is 1.9 seconds. My best 70-90 is 3.1 seconds. Both on 90% charge. These are runs passing through these ranges. For example, the 50-70 was done by starting at 40 MPH and punching it all the way through 80 MPH. The 50-70 is the time it took to pass through it. So it's a lot faster than if I started at 50 MPH and then punched it from that point to 90 MPH.
0-60/30-50/50-70 comparitive times for 70D/85D/P85D - Page 10
So at best, at best, the P85D accelerates from 70-90 as fast as the E90 if you leave the E90 in top gear.
Note: my data is collected using a vbox sport sampled at 20Hz and an external roof mounted antenna.