There is no one single best load R. The only rule of thumb is you'd like the load to be about 10X the value of the internal resistance of the cartridge, or greater. When you go below the 10X ratio, you begin to lose both gain and HF response. The lower below 10X, the worse the phenomenon. And paralleling resistors on either side of the SUT is fraught with compromises and side issues; I wouldn't do it. I hope you do also know that if you start at 470 ohms, using a 1:10 SUT, you cannot achieve any load R greater than 470 ohms. Any resistor you place in parallel at the input will lower the load R. Some swear by silver transformers and others prefer copper windings. There is no consensus on that except silver is apt to cost a lot more than copper. Ypsi make a 1:10 SUT that is likely to be well suited to your phono stage; that's what I would recommend if you are willing to spend the big bucks. Personally, I think the SLP05 is the weakest link in your chain, and I would go for a slightly higher gain linestage, if it were me. But maybe I am being unfair; I haven't heard a Cary preamp in years.