Dynavector 20 Xl , Benz Micro Ace SL or Denon

Nah, buying a better TT he has to buy a new cart anyway!!! then its 3thousand plus..Geez..
As for your question: the Dynavector is very tall.. so you may need to raise the arm base a 3 or 4mm to maintain VTL. The Benz is good, (I have a Benz glider medium output on my P5 and it is a wonderful combination, the Micro Ace on your P3 would be just right, though I would get the medium output as one needs an exceptional phono section to use a low level Benz without noise. (You might also need to raise the armbase 2mm with the Benz, I have to raise mine 2mm for better VTA) The Rega cover should handle up to a 4mm increase in armbase height.
A lot of folks use and like the Denons.. but I have no experience with a Denon cart. (the Denon probably would not need an arm base height adjust.)

The Denon 304 is very good, I have one on my Aries with 12.7 arm. The AT 33 is also a good cartridge, I just got one for $400 at J&R. I got the EV version, also comes as the 33 PTG or something, could never find out what the difference was. You might consider a VTA adjustment base for the Rega, which is a good arm. VPI and Michell and others make them. Don't tell Raul but I find that MCs give more detail than MMs and a better sound stage.

I also have a Benz glider on a P-5. Before this I had an Exact2 on there. Night and day difference. I also had the P3 before upgrading to the P5. The P-3 is a good table and deserves a nice cart!

Hi. I have a modded P-25 (VTAF, etc. which allows different heighted carts) and have used Denon 103r, Shelter 501, Goldring 1042mm and Super Elys carts. I installed the Dynavector 20XL a few weeks ago and while the soundstage isn't quite as wide currently as on some previous carts, I must say this is my all-time favorite cart right out of the box! The sound is just "right" and the soundstage is deep. I listen mostly to rock, pop, and jazz and the cart sounds wonderful with all. I use a Jolida phono stage with upgraded tubes and the table, cart, and phonostage just seem to mesh extremely well. I think this is a cart that I will cherish for the distant future instead of getting that upgrade-itis - it is that good. It does well with vocals and just everything I've put on from Warren Zevon to Steely Dan to Mott the Hoople to Jimmy Smith, Oscar Peterson, Ornette Coleman. I'd read about the Dyna/Rega symbiosis and I am so happy I chose this cart instead of the MM Ortofon 2M Black (which should also be pretty darn good, but doesn't take advantage of my being able to use MC carts and adjust loading and such). Good luck and please report back when you decide.

I second the Dyna 20X recommendation above. I use the HO version and I love it. It is dead quiet in the groove, tracks like a demon, and the sound is musical and very well balanced. It simply sounds "right" to my ear. In my system I preferred it to my Benz H20, and the Benz is twice the price!

So much of this stuff is synergy, so maybe a dose of that came into play and drives my preference. Impossible to know if you will get the same results comparing the two in your setup. My setup is Townshend Rock Mk3 table, Kuzma Stogi Reference arm, and Vista Audio ACLE phono stage.

Unless there is some sort of compatability issue, I can't imagine anyone not appreciating the sheer musicality of the Dyna 20X.

Good luck!