No really the upper limit on human taste is about 80 IBUs. But there are beers out there that boast such things as 200+ IBUs.
As for a partial boil it makes no difference. The bittering comes from boiling hops in the wort. So all you really need to do is add more hops. Of course what kind of hops depends greatly on your tastes and the style of beer you are making.
There is actually a limit to the bitterness that your tastebuds can recognize. I think it's around 100 IBUs, any more than that isn't going to register on your tongue