B&W 804: Big improvement over 704?

the 704s are definitely an aggressive speaker in the high end. The 804s will give you a more balanced sound, but are still prone to sounding bright if the electronics lean that way. As someone who's been wedded to the B&W brand for a long time, I'd suggest being really sure you want to stay with them since you are at a point of making a change.

I have owned several paris and still own a pair of 805 Signatures and a pair of Nautilus 804.
Your speakers are definately forward, i would never call them bright or harsh.
They are very easily toned down with cabling or tweaks.
They should be a pretty big improvement over your current speakers.
I would highly recommend them as i would like imaging, detail and accuracy over the opposite any day.
Good luck and have fun.

Budget?

Take this opportunity to explore and audition outside the B&W line so you will be confident with whatever you end up doing. Check out the usual suspects, Von Schweikert, Vandersteen, Devore,...