Most splitters unless very large industrial have a 24 inch throat meaning it will accept a 24 inch log... Not sure of you concerns of length of logs, when most consider fireplace size around 16 to 18 inches....
Higher GPM rate usually means faster cycle time...... Fast is not always better as you physically may not be able to keep up ....
20 ton is minimal, I have 22 ton standalone and I get some really knurly hard oak and that almost tells splitter it isn't going to happen, but usually does, EXPLOSIVELY!!!
Only negative is it can not go vertical for logs that are too big for you to lift into bed of splitter... Cant use tractor FEL to lift log into splitter because it's on other end of tractor....