I have owned both of these, and I still own the 2028 (four, actually).
Either would be fine for your tank. The 2075 is bulkier than the 2028, so it'll take up noticeably more room in your stand. I ran a 2028 on a 45g tank and the flow was so strong I had to modify my spray bar to knock it down. On a 55g it'd probably be just fine. The 2075 will have noticeably more flow, probably to the point of too much.
I personally like the Pro II series. I don't feel that the modifications made with the redesigned Pro III series warrant the additional cost...however, I think I'm not the only one because I've seen prices on the Pro III drop DRASTICALLY.
My opinion, go with the 2028 unless you find a deal on a 2075 that makes it the same price or cheaper than the 2028. I know what you're thinking: "Should I spend the extra $30-$50 and get the next better model?" and then you're worried that if you "cheap out" you'll regret it. You won't. Don't think of it as the higher model, but rather a different model that happens to be more expensive.