You would get way more than 10FPS running at full resolution at 24 bit color. somewhere around 60FPS is what you would get.
Just make sure the P4 you get has 8MB of octal SPIRAM and you will have more then enough for the 2 full frame buffers to be able to utilize the DMA transfers.
I was doing a little bit of reading on the P4 and as it turns out it has a 2D graphics accelerator built into it called dave2d which I believe that LVGL has a rendering driver for that. That will speed things up quite a bit. Another thing is the DSI driver in the ESP-IDF will allow you to pass smaller partial buffers to LVGL and it handles the copying of the partial buffers to the full buffers using the accelerator which will greatly boost performance as well. You can set it up so LVGL runs on one core and the display driver runs on the other core.
I have to check and see if the SPIRAM is able to be overclocked. I would imagine it is. In order to do that you have to make sure you get the MCU that has at least 8MB of octal SPIRAM and 16mb of octal flash.