You should ideally get an amp no matter what the HU. The RMS ratings of all these HU are similar to a better HU does not means you won't need an amp.
As far as the HU are concerned, 9850 has Bluetooth and a better display/look but 9650 is active capable. Personally I love the specs on 9650 but hate its looks (the dual screen sliding mechanism). If you are fine with the way 9650 looks, you should get it as it would give you way more tuning options, some which I think you wont ever need/use. However, finding a 9650 in a good condition is not an easy task since its atleast 4/5 years old. 9850 on the other hand is a new model so relatively you have more chances of finding a 9850 in a good condition.
