Below is the stats listed on Wiki for Vanguard.
HMS Vanguard.
Installed power: 130,000 shp (97,000 kW)
Propulsion: 4 shafts
4 Parsons steam turbine sets
8 Admiralty 3-drum water-tube boilers
Speed: 30 knots (56 km/h; 35 mph)
150k may get you to 31, while 200+k would get you to the 33-34 knot range.
One thing the Vanguard had over the Iowas was a more weatherly and sea kindly hull. So as long as you have kept to the Vanguard hull type (
) your ship will be fine.
USS Iowa.
Installed power: 212,000 shp (158,000 kW)
8 water-tube boilers
Propulsion: 4 screws;
General Electric geared steam turbines
Speed: 32.5 knots (60.2 km/h; 37.4 mph) (Up to 35.2 knots (65.2 km/h; 40.5 mph) on light load.)