Zephyr,
I used to own the Simaudio P-5 and now have the 5.3 pre.Although the P-5 was an excellent pre , the new 5.3 is much better and is even sonically better than the LE version of the P-5. The best thing is that the price is much cheaper than the previous P-5.
According to Simaudio going to the P-7 would give you an added 15% sound enhancement but at a substancially higher cost. Hope this helps.
Cheers