Does it take you over the 252 cap to 263? (this should show in your skill window now)
If so how much of a difference does the extra 28 skill pts make?
If not how much of a diff does 17 skill pts make?

The cap is 200. The mod takes you to 224 for basically 1% extra mana pres. I don't know how they round but basically either all the previous +mod % items did absolutely nothing or this one is no upgrade at all over another +mod % item. The numbers on them are pretty much meaningless, they should have just been +20 + 40 etc etc so there would be an actual difference.

Of course that's a fixed 1% reduction in mana cost, rather than being part of the random 1% - max% of the mana preservation focus effect.