I think this is important to note- mids are not longboard substitutes until you get to around 8-0 (and then is it still a mid?). For me mids need at least shoulder/head high, open face, then you get the nice swooping carves. Under that and there is not enough room for the turns...unless it's really down the line and you're not trying to go vertical at all, jumst pumping roller coasters...I rode a friends 6'6 CI Mid (2 + 1) and it went really well. Felt smaller than 6'6. Not sure how it would go in weak surf. My experience with mids is that they tend to want a little more wave. Not really a long board substitute although i use mine that way sometimes.
IMHO YMMV