length?
Mass of logs, length of travel, wall thickness of the rod, and angle are all important. Can you not use another profile - for example - "I" beam? The amount of work done is proportional to the distance the log is raised.
I was a sawyer for several years back in the 1960's. Never saw steel tubing like you describe used as part of end-dogging. We milled 20' bucked Quercus rubra logs, 36+" diameter - imported. We milled largely quartersawn 15/4 - air dried and planed to 12/4. We made church pews and furniture.
So I can tell what you are doing:
Will the logs roll up the incline, or are they to be dragged along the length? Unless things have changed radically, you are going to need lots of those (my current opinion) somewhat puny rods. If you are not milling log run, you have to reposition logs during the milling process and re-dog them in place. Log run also requires repositioning for some kinds of mills. So how does the mill hold the log during cutting?
Once you run logs through the mill you have the problem of getting them off there out of harms way, and then stickered (ventilated stacks), which means lifting as well.
So.
1. what exact rod stock are you planning on using?
2. How long do you need the rods to be?
3. Is this a one-man operation? If required, one man cannot usually reposition heavy logs easily and safely. Even with a pinch bar.