Here are a couple suggestions that would work well with your .40...

Lanier Dominator - This should be a fairly straigforward build and the plane is light enough that your .40 won't have any trouble hauling it around. Should be as easy to fly as your 4* but handle a little better and go a lot faster.
http://www2.towerhobbies.com/cgi-bin...?&I=LXNS16&P=0

Sig Cub - This one would be a little more difficult to build but you will learn a lot in the process and end up with something worth looking at. It will also be a little harder to fly so it will teach you a few things there as well. They aren't necessarily difficult, just different than a common sport plane - a little harder to take off/land but flying is fairly straightforward.
http://www2.towerhobbies.com/cgi-bin...?&I=LXFF96&P=0

For something a little more advanced and out of the ordinary but not necessarily the easiest kit build...
Lanier Shrike .10 - I have one powered by a .40 LA
http://www2.towerhobbies.com/cgi-bin...?&I=LXX402&P=7