I do have some hickory and other types of tree that are hard to split but I'm sure the trees in Illinios of the same types are about the same. That said its the hydrolics, (not the PTO power unless you put a pto hydrolic pump on the unit and then it gets a bit pricey) that power the splitter and when I did the math, considering the PSI my tractor hydrolics produces, the size of the cylinder the Countryline has etc, the tonage came out between 12-15 tons. I've never used the Countryline but I have used a 12 ton splitter and it really wasn't up to the job. My Tractor is fairly new but maybe your 35 hp tractor has higher powered hydrolics, if so you could possibly get almost 20 tons out of the splitter, that's a big difference. I did talk to some other people that have used this Countryline splitter, including the salesman at TSC, and they weren't impressed by it, saying it was underpowered but then again it depends on the hydrolic system of the tractor, not its rated HP. TSC represented the Countryline as a 20 ton splitter but I couldn't get close to that using my tractor.
SpeeCo makes this splitter (the Countryline manual even shows that an the end) and the manual shows specs for different cylinder options up to 5 inch, which can produce up to 34 tons at 3200psi, but the only models I've seen for sale, including the Countryline model TSC sells, were those with a 4 inch cylinder.
At any rate one should be careful to consider the specs on ones tractor in conjunction with the specs of the splitter before considering a splitter that runs off of the tractor hydrolics because the performance will vary a lot depending on that information, especially on smaller tractors. I think thats an important thing for anyone reading this thread to know.