Using an image of some kind is the only way to be certain that your table is consisent across all devices and apps, There are quite a lot of them now, on top of which there will be plenty of people who have missed an upgrade somewhere. Even if you are testing using the Previewer supplied by Amazon, you'll find that it handles tables more successfully than the Kindle 3.
As for how professional it looks - that will depend entirely on the quality of the screenshot. Personally, I would put it at the end of the book with hyperlinks to and back. The way the text breaks around an image is entirely unpredictable - it may change if the reader changes the size of the text.
My impression is that readers don't pay much attention to file size any more, though they may have done a couple of years ago.
The fact that you are asking this question suggests to me that you may need to think through your assumptions about ebooks. They are supposed to be universal, as indeed is html. Don't get bogged down in the detail of what you want the reader to see - you can only control the layout in the broadest possible way.