Need recommendations on 4 layer board
You will hate yourself when it comes to board bring up if you have all the important stuff on a buried layer, it makes both probing and the addition of roach wires much harder then it needs to be. 

The standard stackup for 4 layers that nearly everyone goes with is signals on the outer layers, ground on L2 and power (and possibly non critical signals on L3), note that the fast stuff then ends up on L1 with the silicon (Hence no vias in high speed nets), you cannot route it on L4 unless you can organise a local reference plane under that bit of board on L3 plus appropriate stitching. 

I would note that reference planes do not need to be ground, a well decoupled power plane is as good, but remember to get decoupling where the signal changes reference planes. 

Buried signal layers make sense once you get to about 8 layers, but on a 4 layer?. One comment I would make is that thinner layer to layer spacing between the ground and high speed layer (whatever one it is) is a huge win both from an EMC and a SI perspective (It also makes your controlled impedance traces thinner), find out what your board house can do here.