I would take the V4 anytime...a bit more to drive than the new ones but worth it. Keep in mind that there are a lot of other speakers in that price range that compete very nicely, however with your question I would look to save money and get a very nice V4.
They changed the drivers and crossovers...pretty much a new speaker. The new Mini is not the worst of the new Monitor series however it's not any better (though different) than the V4. All of the Monitor series have become more efficient to produce more volume with less grunt. Meant to get the most from cheap AVR's. However that compromise changed the sound of the speaker and not for the better. If you have the extra few bucks I would look at the B&W 685...killer speaker for just a few bucks more.
Art is right, the new V5's are a completely new speaker in every way possible. New drivers and crossovers, made in china now, instead of Paradigm making them. They sound like a bag of smashed a$$holes compared to the V4's. They are cheaply made, and very dissapointing giving Paradigms reputation of great speakers for a good price. The good news is that Paradigm is really focusing on their Studio and Signature series speakers, which are better than ever, and still made, fully in house, in Canada. Neil, save the pennies for a bit longer, and buy the Studio 20's.
I heard the Studio 20s and MM with Yamahas and Denons at Sixth Ave. Electronics. I spent a lot of time and listened carefully. The Paradigms won out over everything else. I have an NAD receiver that puts out 40 WPC which is really all the power I need. Can I power the Studio 20s on only 40 watts?
Is your NAD a 3020? Then maybe, as long as you don't need much volume. That power doesn't really wake up the 20's, I think. It all depends on what you hear, NC.
You can power both the Studio 20's and the B&W's with 40 watts, just don't expect live concert volume. I'm powering 4 ohm sealed B&W 610i's with a 30 yr old 40 watt per channel Sansui receiver and it works beautifully.
Its what you want to pay, Neil. If you want these speakers, you must factor in the stands. Art, how about stands? Neil, Art ran these speaks with a Rotel amp to very happy results.
There are a huge variety of online stores for stands but if you're buying from a dealer I'm sure they have recommendations if not a good 20-24 inch metal stand should work fine.
As far as a good price for used ones I don't know, haven't bought them used. Whatever you are willing to pay is the best price. Seems like your range is reasonable but I haven't looked to see what the demand is on that speaker.
A 24" would put the 20 at ear level with a standard height chair. Gotta keep the tweet at ear level. The only time I heard the 20's with Classe power they had very heavy stands.
Just my two cents about v.5 Paraidgms. I've heard both and own version 4 mini monitors. At first the v.5 seems to be alot clearer and open, but I can't listen to them for a long time because they sound too biased to the highs. The v.4 mini is a little the other direction. They sound a little too dull. In the end I thought the v.4 won out because too dull to me is better than to sharp and bright. The v.5 monitors sound really agressive compared to other Paradigms. I recommend staying away from Denon if you get v.5 as Denon will amplify these annoying traits.