I have a test here of a 98 Explosif showing a bare frame weight of 4.63lbs and I have another test of it somewhere showing similar. I have other tests of the 98 Caldera and Lava Dome giving weights of 4.8, so it wasn't much lighter and I've always assumed that they used the potential of 853 on strength rather than on light weight.
But it just depends what tubing you specify - the other bikes in that first test (all 853) were a Saracen Kili at 4.74 and an M-Trax at 4.17. I also have here a test of a Rock Lobster (UK) 853 with a weight of 4.2. My own RL 853 weighs 4.2 and has a very lively and racey ride, implying that unlike Kona they used 853 for light weight, rather than strength.
The 97 catalogue quotes the Hot at 3.9 - I'm not saying that was true, as it also quotes 3.9 for the Kilauea and mine weighs 4.2, but it still implies that the 97 frames were a bit lighter than the 98s.