Cary SLP-05 Tubes- Matched Quads or Pairs?

For the CarySLP-05 preamp has anyone used different brand matched pairs for slots 1/2 and 4/5?  
These are the L/R positive phase and L/R negative phase sets.
Is a matched Quad best or can you mix two different sets of matched pairs?  Thanks.    

I use matched pairs of 6f8g tubes in all positions except for 6 & 3 where I use a matched pair of Marconi BL-63.