Optimum Size For Previews

I just bought the software. I have tried others, but the speed is hard to beat in MP.

Im not really concerned over space. I have lots of it on external Raid Drive. However, for the catalog I still want to keep it small as possible, but still have viewing value. The reason to keep it small is so that I can copy it at times to my MackBook Pro so that I can keyword and rate files away from home.

The Keyboarding does not really require a great image, but If Im going to be looking through the actual pictures to select which one I want to edit at a later date, then I need to see a decent preview.

I have already determined that for me I need to keep Quality Set to High, and that I really can not go below 1024.

So Im debating the 1280 or 1920 sizes. Kind of wish they had something about 1400-1600 but I do not see it.

Questions:

1. Within MP I see an option to show the SIZE in Bytes of the thumbnail, but none for size of the preview. Is there one?

2. How can I find, or determine the rough size that a 1024, 1280 and 1920 take, in general?

3. Out of curiosity, what size do some of you use for previews, and if you do a lot of offline work.

Thanks In Advance
Craig.