Combat radius per USAF requirements (take off, climb to 25000 ft, cruise at 210 mph indicated air speed, 15 min of combat on military power, 5 min of combat on war emergency power, return to base at 25000 ft and 210 IAS, 30 min reserve) was 700 miles for the P-51B/C/D/H and 1000 miles for the P-47N.
Source: USAF table found in 'America's hundred thousand', pg. 599 and 600.
Combat radius per USAF requirements (take off, climb to 25000 ft, cruise at 210 mph indicated air speed, 15 min of combat on military power, 5 min of combat on war emergency power, return to base at 25000 ft and 210 IAS, 30 min reserve) was 700 miles for the P-51B/C/D/H and 1000 miles for the P-47N.
Source: USAF table found in 'America's hundred thousand', pg. 599 and 600.
Internal and external fuel. P-51 carrying 2 x 75 gals DTs, the P-47N with 440 US gals of fuel in DTs ( 2 x 165 plus one 110 gal). Remark is also made that P-47N can beat the 1000 mile mark when using 2 x 300 gal tanks, but gain was just 25 miles in that case.
With internal fuel only, under same requirement and allowances, the radius was 375 miles for the Merlin Mustangs, and 400 miles for the P-47N. For comparison, the later versions of P-47D were good for 600 miles when carrying 2 x 150 gal DTs, and 225 miles with just internal 370 gals.
Note that the ranges given for P-51B/C in the tables above include only the 2x75 gallon tanks whereas the P-47N includes 2x160 plus 1x110 gallon tanks. The Mustang carried 2x160 gallon tanks in the PTO and for cruise settings/combat assumptions had (IIRC) approximately 950 mile combat radius.
The continued drag advantage of the P-51B/D over the P-47N is illustrated by comparing the Combat Radius charts with internal fuel only (556 vs 269 gallons) to gain only 25 mi advantage (400 vs 375).
With an external bomb load of 2x1000 pound bombs the P-51B/D had a 50 mi advantage over the P-47N (350 vs 300mi)
The P-47N can carry two 1000 lbs bombs and a 110 gal tank and still be under the max TO limit, with obvious increase in range/radius. Or two 1600 lb AP bombs and a drop tank, if you want to do some Yamato-hunting. Or 2 x 2000 lb bombs?
The cruising setting above Pacific ad above Axis-held Europe were different - since there was no fighter or Flak danger many miles from Japanese-held territory, the cruise requirements could be relaxed to, say, 10000 ft and 120 mph IAS with appreciable rise in radius/range.
The table noting 1310 mi combat radius for P-47N: link