Scot, if the pushrod is a continuous wire from end to end with plenty of guides stationed to prevent bowing or flex, that's all you need. Carbon tubing slid over the wire is great for applications where guides aren't practical or would look too "cobby".
Modelers got along just fine before carbon tubes came out. The extra mass of unsupported carbon rods can also start vibrating at lower than expected rpms and wipe out a gear train if conditions are just right [or wrong].
For .40 to .60 sized planes, #4 hardware will usually outlast the plane...but keep your eye on the clevises. Steel clevises VS nylon is a subject for debate, but both work. I like the nylon clevises that have a steel pin.
Check your installation out in both push and pull mode by fighting the servo's effort with reasonable pressure from your hand. There shouldn't be any give, slop, clicks, pops, snaps, grinding, smoke billowing, etc.
Have fun.