To the OP: the choice between the Allant+ 7 and 8 really comes down to your personal preferences, what type of riding you plan on doing, and your budget expectations. I own a 7s but have also ridden the 8s on a couple of test rides.
The primary differences between the 7s and the 8s are:
- 500 Wh battery(7s) vs 625 Wh battery(8s)
- Mobie 25 suspension fork(7s) vs. AL rigid blade fork(8s)
- Shimano Alivio 11-36t 9-spd(7s) vs Shimano Deore 11-42t 10-spd(8s)
- Purion display(7s) vs Smartphone Hub display(8s)
- Herrmans/AXA lights(7s) vs. Trek Lync lights(8s)
- Racktime Lightit rear rack(7s)vs. Lowrider (panniers only) rear rack(8s)
- Schwalbe G-One tires(7s) vs. Bontrager E6 tires(8s)
- Price
If, as your original post indicates, you are considering the 7s (Bosch Performance Line Speed, 28mph) versus the 8 (Bosch Performance Line CX, 20mph) there are additional differences to consider. First and foremost you should ask yourself if you want/need the additional speed support (20mph vs 28mph). Do you regularly exceed 20mph on an analog bike ride? On steeper uphill sections both motors will be the same since you won't be riding over 20mph uphill.
The primary differences between the 7s (28mph PL Speed) and the 8 (20mph PL CX) are:
- Bosch Performance Line Speed, 28mph (7s) vs. Bosch Performance Line CX, 20mph (8)
- Shimano MT520 4-piston hydraulic disc brakes (7s) vs Shimano MT200 hydraulic disc brakes (8)
- Mobie 25 suspension fork(7s) vs. AL rigid blade fork(8)
- Shimano Alivio 11-36t 9-spd(7s) vs Shimano Deore 11-42t 10-spd(8)
- Purion display(7s) vs Smartphone Hub display(8)
- Herrmans/AXA lights(7s) vs. Trek Lync lights(8)
- Racktime Lightit rear rack(7s)vs. Lowrider (panniers only) rear rack(8)
- Schwalbe G-One tires(7s) vs. Bontrager E6 tires(8)
- Price (but only slight difference ~$100)
For me, I was only considering class 3 (28 mph) because I preferred the option of having the additional speed when I need it (on roads I frequently ride above 20mph and wanted the motor to support). You can, of course, ride above 20mph with the PL CX motor, but the motor will not be helping you at those speeds and it will be a lot of work (unless you are going downhill). I also really love the MT520 4-piston hydraulic disc brakes that are on the Speed models (both 7s and 8s), but both sets of brake models (mt520 and mt200) are well matched to the bike and should have no problem stopping you. I liked both the 7s and 8s. If I had unlimited budget I probably would have gone with the 8s, but the 7s met all of my criteria and I am very happy with the bike.
I wouldn't worry about the 3lb weight difference between the bikes. That is negligible in my opinion.