There is an overlap and there are differences.
Overlap. At the core of both an investor and a sales presentation is some story that said what it is you actually do, and why this is such a great solution that you should buy it. Useful for a customer, but also useful for an investor. The latter will ask: "will someone want to buy this?", but more importantly: "can this person sell in a convincing way?" This overlapping part of the presentation is the core company story.
Sales presentation only: add things that are specific to the potential client's problem/situation. Add a censored competitive positioning (don't bend the truth, but don't volunteer weaknesses either). Add the administrative details about exact pricing, installation, etc. etc.
Investor presentation only: add a (more) candid competitive positioning, market sizing, profitability, pipeline, team bio, etc.
So, the investor presentation is the broadest in coverage. In terms of number of slides (hours at the computer), each of the above components could be equal in size. In terms of time invested though, the first part, the core sales presentation is the hardest to get right, it is the fundamental story of your company/product.
Bonus, a quick Venn diagram in SlideMagic style (make decent looking simple slides quickly) below. You can clone slides I used in the blog to your own SlideMagic account via this link.