You can find frequency response graphs on both here:
http://www.head-fi.org/t/605438/sennheiser-ie800-iems/255#post_8695393
It confirms the boosted sub-bass and also the mid-bass hump plaguing the IE80 has been fixed. Highs are also less peaky, so it should be ok. I can´t test my IE8 right now as I have no cord for it (cat bit it in half), but from memory I would definitely say the IE8 is brighter than the IE800, more of a V-shape sound signature. No idea about IE80 though.
Mimouille: Depends a lot on the country... Here in Finland if I order from outside the EU, ordering the Heir 8 would actually cost pretty much exactly the same as the IE800 (usually 1-5% and an extra 24% VAT; and this is all calculated from the total cost, including shipping!). The end cost is within 100 euros (IE800 is 700 euros in the EU, so it´s not one of the usual dollar = euro ones) and if I ever have warranty problems with Heir Audio that would be a very expensive thing too. Sennheiser´s warranty support works great and at no cost to me. The VAT and customs are so high these days I am basically limited to products I can buy from Amazon.de or some other store within the EU. This cuts out Westone 4R (overpriced and warranty is difficult) and most customs. Now that EX1000 is almost nowhere to be found in the EU anymore (one online store in Finland sells it for 800 euros) the IE800 is pretty much the only easily available high end dynamic driver IEM.