My thought is that a Mamba 7.6 would likely be too small. You could probably squeeze into it, but it would be less than ideal (especially if you plan to creek in it, since the relative lack of volume for your size would probably negatively impact the boat's ability to resurface quickly).
I am close to your size (5-8, 155 pounds) and paddled a Nomad 8.1, which is comparable in size to a Mamba 8.1, for a few years. I thought the sizing was about right. The 8.1 is not a big boat by any stretch of the imagination, especially compared to newer creekboats where the trend is bigger is better. In addition, I've seen lots of guys - and gals - who are about your size or smaller paddling Nomad 8.5s or medium Newmads that are slightly bigger than the old 8.5.
In short, my guess is that a Mamba 7.6 is WAY too small for you. Hope this is helpful to you.