Cutting concrete is dangerous M'kay. Ask me how I know. I know of 2 guys that died, one that was rockerd in the head with a drill down inside a manhole, I have been in the hospital when my hand was cracked and swelled to the size of a grapefruit, almost died of carbon monoxide poisoning twice, and of course we all know my latest injury which terminated my career.
And as Shief stated a 35hp saw is good for probably up to a 24" blade, you could use a bigger blade and it will hold it(maybe not out of the cut but you can attach it in the cut) but you wouldnt want to go much bigger or use it all day long. The 35hp saws tend to have a smaller arbor plate size so you actually go deeper with it than the size on a 65hp saw. It would be harder now eo find an original 35hp walk behind. If all your looking to do is have a saw for control joints or light cutting a pushsaw either manually propelled or self propelled is the way to go. You dont go but 5" deep with them but you can always add a blade in the cut to go deeper.
Shief pre cast walls are the absolute worst to cut, harder aggregate and when you hit a tension cable, forget about it. Who are you working for now? You should have came over when I was trying to get you on. Ohio concrete is the best around.