Yes it is totaly possibe to get higher speed, but you should delid before you even thing of using a water chiller. You could probably get 5ghz easily with a water chiller. It costs quite a lot to set one up considering the temp drop . You're better off buying single stage phase cooling which is much lower temp than chiller, and will allow you to go much higher in cpu ghz.
Delliding can drop the temps by as much as 8c with the same cooling, so consider doing that first. There are delidding tools available that let you delid the cpu risk free. You can do it using a blade which is like $0.20 which is a cheaper option but you will be risking damaging the cpu.
at that voltage, no. That is actually very decent for an aio