Welcome to WebmasterWorld Louie ;)
I doubt this would be a problem at all, as long as the site(s) are not complete mirrors of each other.
However, you may want to look at diversifying your themes (keywords) as a better way to target.
Example: being ranked 1, 2, 3, 4 or so on may seem like a good approach but if the visitor clicks on #1 and finds what they want, 2 through whatever are wasted rankings.
The flip-side of this is if the visitor clicks on #1 and doesn't find what they want, in all likihood, 2 through whatever is more likely to produce the same results.
Either way diversity in targeting more keywords (rather than the same ones) will produce greater fruition is the same period of time.