True, both boards will be fine but I think you can be just as aggressive freeriding on either board but the 145 will give you just a little more playfulness to make buttering less of a chore. Then again, there's something to be said about learning to flatland it on a more difficult board. Of course, we could also snowboard with weighted vests to further our skills but I don't think anyone does this. I can butter my friends Arbor Element RX - but it's not particularly fun.
I think the offset in playfulness going down will outweigh any of the tradeoffs: barely noticeable reduction in aggressiveness, barely noticeable reduction in float in powder.