I could write a book about this topic. In short, temp probe helps considerably on any body of water. I have the Fish Hawk X4, you dont need the X4d. Mind you I fished for years without it. As long as you have a good graph that shows your cannonballs you should be ok. I like having it because I find its interesting to see how and where temps change and why. Some places on the Bay current isn't a huge factor in fact most places it isnt, its nowhere near as bad as Lake Ontario. Its when you start fishing structure and in rough water then speed at the ball is vital.
Case in point just last night I was going 1.6 surface and getting 3 at the ball fishing tight to a drop. I use 16-20lb balls so not much blowback to judge the currents.
Hope this helps