I'm surprised to see that much difference between IE6 and IE8.
Though IIRC the sunspider test is all javascipt processing and no DOM manipulation, so perhaps the fact I pecieve IE8 as not being that much faster may mean that its DOM layer is the bottleneck I'm experiencing. Not unlikely as I don't currently do large amounts of nmuber-crunching and text processing in anything I have to test under IE.
Yup. Here's a chart to put IE6 v IE8 v IE10 javascript engine into perspective: http://goo.gl/3ACqo