I would get the 70-200 4 IS, the reason being is that it is $600 cheaper then the 2.8 IS, much lighter and smaller. The 70-200 4 IS is ~ the same size and weight as the non IS. If you decide you do need the 2.8 save up and get the IS one. The reason is that the two IS 70-200's are fully sealed against water dust, where the two non IS ones are. The 70-200 4 IS is also the sharpest of the series.
I would go with the 70-200 4 IS over the 2.8 IS due to price and size. It is much easier to carry the 4 IS around then the 2.8. Also with the money you can get a 85 1.8, a 15mm 2.8, or almost enough for a 135 2.0! (which is money!)