Check out Brian Enos' site. He says the handle of your press should be shoulder height. I thought that was too high because I had loaded on a RL550 for years that wasn't near that high. When I purchased my XL650 I sat it up as he suggested and it makes a world of difference. So much I went back and ordered a strong mount for my 550 too in order to get it higher.
My work bench is 36" tall but the hight of your loader's handle is probably more important. I also use an adjustable stool with mine.