Nautilus owners upgrade to what?

obviously, it depends on your other equipment as well as your music preferences, but I have B&W Nautilus 803 as well as totem mani 2, revel f 50 and aerial 8b. I like/love them all, but for different moods. The aerial is a little smoother than B&W, the Revel a little better at revealing the top end, and the totem is strong in the midrange. I kept the B&W, so you can judge for yourself, but I would audition the others based on situations. Good luck.

LM Frog, you really use 250 watts with your B&W 805's?
Jeez, my Musical Fidelity's 120 Watts seems like an ass whup when I crank it up on mine.

Thanks all for the input. That's interesting about the high markup on B&W. So overall it sounds like my 804's are a pretty good product.
I will try some of your suggestions -Karma and Audio Physics, Revels, and ProAc Futures maybe. I also found a dealer who carries Dunlavy so will try them out.
Will have to do some searching for the Piega, Totems, and Avalon as these aren't so common in New England.
My amp is a 120 wpc Musical Fidelity and I think the B&W could soak up 200 wpc when it comes to rim shots and thumping bass. Budget is around $5,000 max. The 802's sounded great but I can't justify the $5,000 premium over the 804's.

Oh, c'mon, sure you can! Money is fleeting, but those 802's will be "forever" :-)

I would search for 804 in speaker forum first.
I own (and love) 805, and to me, and several other A'gon posters, if memory serves me correctly, many people have preferred the 805 to the 804, and if you have that kind of $$, 805 matched with a REL (I think the Strata III is the proper match) subwoofer will get you near pinpoint sourcing that the 804 can't match with the much more spread out drivers, and a MUCH better bass response than the 804. CHeck the stats on teh B&W homepage, teh 4 doesn't go much lower than the 5, and side by side, the 5 sounded more integrated and less artificial.
good luck.