A friend of mine has the 8.2 Diamonds, and they sound very muffled and fuzzy to me. Supposedly the 8.4 is the best of the 8 series, and the 9 series is supposed to be better than the 8 series.
With Polk I wouldn't bother with the Monitor series but look only at the RTis and if budget allows, the LSis. Neither though really offers great value for the money.
I differ from Edster opinion. (Respectfully) I own a pair of Polks RTi12's ( I paid $2800.00 for both) and IMHO they are a great value for the money and perhaps under rated, I am sure there are better and more expensive speakers out there but for the money believe me they sound great. I am driving them with a NAD C-162 pre-Amp and two bridged NAD C-270 Amps.
If you can, go and try to audition, only you can decide which one sounds better to your ears.
Obviously, more of us have experience with the Polk speakers...who has the Warfdale experience we need on this question? incidentally, I love my Polk RT1000i's. They fit my budget at the time 6 years ago and I have used them for both music and movies.
I have Warfdale pacific evo's (evo40,10, center). These speakers are very laid back with a nice warm sound, but the center IMO is too laid back for a center channel and I will be looking to replace it with something a little louder. Previously I had a Klipsch center that wasn't tonally correct for the rest of the speakers, but was plenty sharp enough for movies.
Bottom line. Warfedales sound nice with some good low bass (out of the 40s), but the center wasn't clear enough (way too laid back). Pair them up with some of the brighter amps (my Integra 7.4 is bright compared to NAD and Rotel). Look for a different center...although I don't have experience with the diamond line's center.