I’m trying to figure an accurate estimate for putting in a 4ft high Field Fence, but I want to use a 2 piece chain link Gate from Home Depot. I was thinking of using a 4x4 posts even for the cross brace, but I’m having second thoughts after seeing it drawn out in Sketchup.

What do you think and should I do this differently?

Switch the angle of your braces... Keep the strength against the sag of the gates.

Thanks It did look a little weird to me but at first I was thinking of using a steel cable as my brace and stayed with the same direction for some reason.

I'd use the stainless cable you described, with a turnbuckle. That way, you can tighten it up later if you need to.

Thanks,that just might also solve my problem of fastening the 4x4s together. I was thinking of using really long lag bolts or maybe those sheet metal brackets.

Might eventually need to run the cable on the gates themselves to correct any sag they acquire over time.

Hmm you may be right. I didn't think of that. Funny that the gate doesn't come with that for the amount of money it costs.

I would go with two cables that cross in the center to tops and bottoms of the posts. Really doubt a 5' steel gate will sag.

I don't think anyone's saying the gates themselves will sag, just that the weight of the gates could cause the post that it's attached to to curve, causing a sag like effect.

The cable idea sounds interesting but I think a 2x4 brace would be just fine. Just change the angle/direction of the one in your picture as was mentioned.

I replaced the 4x4 braces in Sketchup with 3/8” cable and now I’m wondering if I really need the top 4x4

Here's a bit of first year engineering regarding trusses. The loads from the gate acting on the gate posts are such that the outer top 4x4 and the outer post are what are called "zero force members." In other words, all the loads will be carried by the cable and the other two members are not doing anything but looking good. Your intuition is correct.

the top members are providing more than just a support for the gate post. I think the top horizontal members will add stability to the fence overall, esp providing a tie point for the top of the "field fence" material.

I like the idea of the top horizontal 4x4 as a design element in the general appearance of the fence.
It completes the frame concept with the adjacent posts.
My back-alley and side yard gates are sort of like that = I don't know how many times I have needed a flat spot to set something down "just for a minute."

Or, run the verticals up as high as allowed, add a bit of trellis wire and plant grape vines.