"Pushing the envelope": Ger/CL/1915 Very Fast

I have this pencil drawing from 1971 and some minimal specifications. I was "dreaming" when I thought that 50 or 60 knots might be achievable. It definitely is not achievable in Springsharp, and not on 7,000 tons with 175,000 SHP with 45SHP/ton of machinery weight. The ship is 625ft long and is a fast cruiser. I guessed that the armament would be 4-6in guns, grouped forward, as was my preference at the time. This is the resulting Sprinsharp report:

Ger/CL/1915 Very Fast, Enter country Enter ship type laid down 1915 (Engine 1950)

Displacement:
 8,637 t light; 8,865 t standard; 9,600 t normal; 10,188 t full load

Dimensions: Length overall / water x beam x draught
 628.52 ft / 625.00 ft x 62.00 ft x 23.00 ft (normal load)
 191.57 m / 190.50 m x 18.90 m  x 7.01 m

Armament:
      4 - 6.00" / 152 mm guns (2x2 guns), 108.00lbs / 48.99kg shells, 1915 Model
   Quick firing guns in deck mounts with hoists
   on centreline, all forward, 1 raised mount - superfiring
 Weight of broadside 432 lbs / 196 kg
 Shells per gun, main battery: 150

Machinery:
 Oil fired boilers, steam turbines, 
 Geared drive, 4 shafts, 168,902 shp / 126,001 Kw = 39.00 kts
 Range 4,500nm at 18.00 kts
 Bunker at max displacement = 1,322 tons

Complement:
 484 - 630

Cost:
 £1.329 million / $5.314 million

Distribution of weights at normal displacement:
 Armament: 54 tons, 0.6 %
 Machinery: 4,041 tons, 42.1 %
 Hull, fittings & equipment: 4,543 tons, 47.3 %
 Fuel, ammunition & stores: 963 tons, 10.0 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   7,588 lbs / 3,442 Kg = 70.3 x 6.0 " / 152 mm shells or 1.0 torpedoes
 Stability (Unstable if below 1.00): 1.29
 Metacentric height 3.9 ft / 1.2 m
 Roll period: 13.3 seconds
 Steadiness - As gun platform (Average = 50 %): 72 %
   - Recoil effect (Restricted arc if above 1.00): 0.14
 Seaboat quality  (Average = 1.00): 1.43

Hull form characteristics:
 Hull has a flush deck
 Block coefficient: 0.377
 Length to Beam Ratio: 10.08 : 1
 'Natural speed' for length: 25.00 kts
 Power going to wave formation at top speed: 60 %
 Trim (Max stability = 0, Max steadiness = 100): 50
 Bow angle (Positive = bow angles forward): 3.00 degrees
 Stern overhang: 2.00 ft / 0.61 m
 Freeboard (% = measuring location as a percentage of overall length):
    - Stem:  29.00 ft / 8.84 m
    - Forecastle (20 %): 25.00 ft / 7.62 m
    - Mid (50 %):  25.00 ft / 7.62 m
    - Quarterdeck (15 %): 25.00 ft / 7.62 m
    - Stern:  25.00 ft / 7.62 m
    - Average freeboard: 25.32 ft / 7.72 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 140.7 %
  - Above water (accommodation/working, high = better): 232.2 %
 Waterplane Area: 23,602 Square feet or 2,193 Square metres
 Displacement factor (Displacement / loading): 113 %
 Structure weight / hull surface area: 100 lbs/sq ft or 490 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.89
  - Longitudinal: 2.96
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is cramped
 Room for accommodation and workspaces is excellent
 Ship has slow, easy roll, a good, steady gun platform
 Good seaboat, rides out heavy weather easily