Good question. I think the only person I've heard of that might have compared the two is Jeff Dorgay of ToneAudio. He wrote in another forum:
"I think the RP6 is slightly better. A little bit less of a jump than between the P3 and the P5...
The only real way to tell exactly how much better would be to mount an RB 303 and RB 700 on two identical tables, but the RP6 as a package, with an Exact still does a bit better job (especially at low level detail and overall clarity) than a P5 with an Exact.
If you've got a P5, I don't know that I'd trade it in for an RP6, I'd go for a P7 or P9 (especially the P9)"
Notice, however, that he did not say whether the P5 was the stock version or with the TT-PSU.
Regardless, common sense says that if you can get them around the same price (P5 with TTPSU and RP6 stock), I don't think you could go wrong with either.
One other critical consideration: how many LPs do you have, and how many of them are very high quality? Most of my 900 or so LPs are of average or good quality, not the most expensive or highest quality, of which I only have 50 or so. Given that I'm not a snob, I don't have room for many more LPs, maybe a couple hundred more at most, I think that the P5 will do me for the long haul.
If you're in the same boat as me, you likely don't have to worry about any upgrading rollercoaster like so many others.
WT Simplex, Shelter 501 II, DV20xl, Benz ACE SL > Aleph Ono, Bel Canto PL1/DAC3 > Pass X1 > XA30.5 > DeVore Nines
: Beyond measurements and theory, there's intuition and feeling: