The resonant frequency and low SWR point will definitely shift.
When it comes to gain, normally I would expect only a small difference from such a change, however, then I remembered some of the thoughts I had that date to the "blue line" discussion from pages ago, this would effectively cause one of the current nodes to change, and move away from what is an optimal location for it, causing said "blue line" to carry more current, and make the antenna less efficient overall. It still wasn't a big change, but it was more than I would normally expect to see...
Also, SWR on the tuned frequency went from 1.1 to 2.2. Radiation efficiency dropped by over 10%. R went down from about 55 to about 52. X went way down, from near 0 to -41.
Good guess, although the shift was larger, closer to 800 kHz.
I modeled it at one point, it still worked, although the feed point impedance went up as R went from near 50 to closer to 70. I didn't do anything else to adjust the antenna to compensate. I have since made a change or two and modified the size and height of the cap hat to account for tuning changes just to see what would happen.
The DB
