Well, I can't speak for the QXT Pro because I've never used one. But I can speak for the DFX, as a former owner. And although the DFX is a capable and sophisticated machine (and White's top-of-the-line machine) it was never more than adequate on the beach. I used it for 6 months and did well with it but ultimately got rid of it in favor of a Fisher CZ-70 which is a better machine both on the beach and on land than the DFX. And the Sovereign I recommended is better at the beach than the CZ, and that's a tough trick. And the Quattro is better at the beach than all of them, in my opinion. So you be the judge.
As for the QXT having a beach program, most machines do. And many don't work as well as others. And some that don't have a beach program per say, like the CZ-70 and the Sovereign, are some of the best beach machines. "Programs" are generally worthless if you ask me. They are no substitute for a user that has done the time and gained the experience with their machine that comes from getting out there with it and learning it. And these forums will help immensely with that.
Now the Quattro DOES have a beach program. And it's actually quite good and what I used when I had mine. Because it accepts all non-ferrous metals...basically from foil on up, ignoring the iron...which would be rusty things, fish hooks, old bobbie pins, etc. and lets you know about the good stuff, like foil and pull tabs. Which since you said you are new, I will guess that you don't know that those things and other aluminum stuff is the same exact range that your gold and diamond rings come in at. And no, there is no detector that can tell the difference between a pull tab and a gold ring with any certainty, unfortunately. And the Quattro is very easy to use. Turn it on, choose the "Coin and Jewelry" program (that's Beach mode) and start hunting. It goes very deep, even in the factory "Auto" sensitivity mode. But if you get tired of digging up stuff 12" and less deep, you can always set the sensitivity to manual at about 17 or 18 (20 is max) and you will be digging stuff at 18" and deeper. It's pretty amazing.
Here are your adjustable settings with the QXT:
14 User Adjustments
Volume
Threshold
Search Sens.
Pinpoint Sens.
Viewing Angle
S.A.T. Speed
Tracking Speed
Transmit Frequency
Discrimination On/Off
VCO Audio
Noise Reduction
Mixed Mode Audio
Disc. Edit/Zones 1-8
Tone Alert
I'm not sure that is the best setup for a new user. Maybe too many settings to fiddle with and too much chance to screw it up. Now I'm SURE that any QXT owners reading this will say "Ah, that's crap...it's any easy machine to use." And it may be, if you use one of the "turn-on-and-go" programs. Even the Minelab Explorer II has those. And they work, somewhat. But one of the big gripes I had with the DFX was that I spent way too much time fiddling with it and tweaking it and adjusting it (it had 54 adjustable settings, by the way) and not enough time hunting and having fun with it. That said, I know that some have been successful with the QXT and the MXT and other White's machines. And they do make a quality product. I think for your use, and the fact that the beach is going to be your main thing, I would go with the Quattro. Or a Sovereign. And you may well be able to get a nice deal on either of those if you get a used one. I prefer new, with a warranty.
So hopefully there's some info there that helps you.
If you want to look at the Quattro users manual, you can get it in the links below. It's actually in 3 parts.
Here's a link to Quattro info on the Minelab site:
http://www.consumer.minelab.com/default.asp?pageid=PRODUCT&template=PRODUCTCAT&cid=344&pid=1635&site=3
Here are the 3 parts to the manual:
http://www.minelab.com/images/1-0_Consumer/1-2_Products/1-2-12_Quattro/quattro-manual1.pdf
http://www.minelab.com/images/1-0_Consumer/1-2_Products/1-2-12_Quattro/quattro-manual2.pdf
http://www.minelab.com/images/1-0_Consumer/1-2_Products/1-2-12_Quattro/quattro-manual3.pdf