In order to do that upgrade you will need a new CPU, motherboard, and RAM. Given the age of the rig it would likely be best to consider all new.
There is nothing about W11 that is compelling enough to spend that much on in comparison to W10 IF your current build suits your needs otherwise. W11 is W10 with window dressing and bells and whistles. In some ways it is less desirable because of lesser user control over certain aspects, particularly privacy.