Naval News reports that the Korea Coast Guard will be receiving two new cutters. These are reported to displace 4,200 tons full load, meaning they are slightly smaller, but considerably longer than the 418 foot 4500 ton National Security Cutters and 360 foot Offshore Patrol Cutters of similar displacement.
There is no indication of the speed of the new cutters, but the earlier similar sized cutters, hull numbers 3009, 3010, and 3011 were reportedly capable of 28 knots. Armament seems be being standardized at a twin 40mm mount and 20mm Sea Vulcan Gatling Guns, both locally produced.
The Korean Coast Guard currently has 36 cutters of more than 1500 tons full load, including two of 6,500 tons full load, only one of the 36 is over 26 years old. Their Exclusive Economic Zone is less than 2.7% that of the US, but it is complicated by the proximity of North Korea, China, Russia, and Japan.
Chuck Hill's CG Blog 
I bet they are quoting light displacement. Seems to be their MO most of the time.
Asian Nations do tend to minimize the size of their ships. These are classified as 3000 ton cutters, that is why the hull numbers are four digits beginning with a three. The 6500 ton monsters are rated as 5,000 ton ships.
The 4,200 ton displacement is specifically described as full load displacement. We don’t have measurements on this class, but it is almost certainly narrower than the new USCG cutters. They are built for higher speed than the OPCs which have a relatively large beam. The earlier class I mentioned are about 4000 tons full load and have almost 40,000 HP, about twice that of the OPCs and almost as much as the NSC. Being designed for relatively higher speed than OPCs, they would have a higher length to beam ratio. They might have a shallower draft as well. There is also a good possibility they do not carry as much fuel at full load as the USCG ships because their patrol areas do not require great range. So the 4,200 ton full load displacement is believable even given their greater length (assuming the length is reported correctly).
My fave example is the Shikishima-class patrol vessel of the Japanese CG. I am still not sure how much they displace.
@X, What I have for Shikishima is 6,500 tons light, 7,175 tons standard, and 9,350 tons full load. The Japanese are building two more for a total of four. The Chinese have a couple of cutters that are even larger.
The Japanese have far more large cutters than the USCG and like the Koreans, their fleet is much newer.