I have the same engines in my smaller boat.* We are 43' and 34,000 lbs disp.* After exhaustive test runs over the last year I have found there is very little to gain running on a single (although there are no issues with twin disc or Caterpillar) vs. running both engines.* I cruise on both engines (without loading up, etc.)*at around 1,100 rpm and get excellent fuel consumption running just a tad over 'calculated'*hull speed.* Parts are readilly available and Cat service centers have been excellent to deal with.* As was mentioned, at 1,500 rpm I get only slightly less mpg but great performance @ 10 knots*and the engines will run forever at these low rpms, imho.* I am not familiar enough with the 52' to have an opinion, but I like the Jeff's I have seen.
Good Luck