Legend class Coast Guard cutters are listed as 28 knots, max., with a range over 12,000 miles versus the LCS's 3,500 miles. The Coast Guards new OPC has a max designed speed of 22.5 knots, with a 10,000 mile range at 14 knots.
https://www.dcms.uscg.mil/Our-Organization/Assistant-Commandant-for-Acquisitions-CG-9/Programs/Surface-Programs/Offshore-Patrol-Cutter/
I wouldn't speculate on the range of a diesel-only DCS hull, but removing the gas turbine and trouble-prone diesel-gas turbine power combining gearbox, extra fuel storage could be provided.
And keep in mind that the idea (not mine, really) is for the DCS to replace just some of the planned 25 $411 million OPCs. You can do a lot of modifications with a $400 million budget when you get the hulls for free.
"The Coast Guards new OPC has a max designed speed of 22.5 knots, with a 10,000 mile range at 14 knots." Which makes it less capable than the current Legend class:
"The Legend-class cutter, also known as the National Security Cutter (NSC) and Maritime Security Cutter, Large, is the largest active patrol cutter class of the United States Coast Guard.
Entering into service in 2008, the Legend-class is the largest of several new cutter designs developed as part of the Integrated Deepwater System Program.[9]"
Compare to Heritage class:
"The Heritage-class cutter, also known as the Offshore Patrol Cutter and the Maritime Security Cutter, Medium, is a cutter class of the United States Coast Guard (USCG), developed as part of the Integrated Deepwater System Program and built by Eastern Shipbuilding.[4]
Construction of the first vessel in the class began in January 2019."
The two cutter classes appear to be quite similar in size & performance, with Legend slightly longer, wider, faster & longer range.
The Legend class has combined diesel & gas engines and so a higher max speed of 28+ knots, while Heritage has only diesel engines and 24.5 knots max speed.
Given their current issues, I don't see how the Navy's LCSs could ever replace the Coast Guard's most advanced cutters.
Heritage Class Argus:
Legend Class Bertholf: