How high a grit will yield an improvement, and what which brand and series(!) of stone will achieve, is somewhat dependent on the steel and heat treat used in the knife you are sharpening.
A "very old" knife could be an obsolete stainless formula/heat treat yielding a very coarse (and/or unstable) grain- commodity stainless steels and their heat treating were still experiencing development in the 1940s!, OR be sub-par steel from the start, OR have suffered abuse by dry grinding (damaged temper), OR actually be a non-stainless steel (not that likely - with non-stainless even grits up into the 10000s can yield an improvement).
While not the case here, a general answer to this question needs to include the fact that there are different systems of grit numbering (not a problem here since both are japanese style stones - if you had european oilstones in the mix they could easily be of a seemingly lower but actually higher grit, reversing your progression!).
Make sure your deburring is good.
Be aware that a 3000 grit is kind of dual-purpose: It is in the high end of sharpening grits, and on the low end of polishing grits, and can be used in either function. Use technique that matches your choice.
Make sure your final strokes on the high grit stone are very light, and/or try stropping on a paddle, newspaper (no polishing compound needed in either case. final strokes gentle here too!) - both will make sure to align the edge.
For some users, the kind of sharpness you get from a 3000 grit or higher could APPEAR less sharp since it will be potentially less aggressive in slicing cuts but actually sharper in push cuts (try with a sponge - a perfectly executed edge on a 3000 should be able to be pushed into it without moving the edge, a good 800 edge is unlikely to even if it will very likely slice the sponge easily).
If you are testing sharpness by cutting food, some foodstuffs might not feel more easily cut with a sharper knife beyond a certain level of sharpness, since the factor limiting the ease of cutting will be edge and/or blade geometry (including things like behind-the-edge thinness, bevel asymmetry and steering....) and not edge sharpness.
Mind that soft stones easily go badly out of true (even the Chroma stone will ;), and that can affect your sharpening result especially if you are inexperienced. Flatten them.
About "different manufacturers": This is less about manufacturers but about exact stone properties - eg Naniwa will make very soft stones (as you have) and some very hard ones (the pro/chosera series). While there is some interaction between what one stone leaves and what the next can make of it, this is an advanced topic more relevant if cosmetically good polishes are intended; failure to obtain performance from a knife is unlikely as long as each of these stones is used correctly.