Faster load time is questionable - its only faster cause it take less code to load but it would take a looooot to switching from table to div in order to see a significant difference in load time. Removing any image would probably save more load time.
UX-wise... you should test your website in several browsers and devices, in addition to fetching/rendering as google. If everything looks good and is easy to navigate, wouldn't worry about it.
With that in mind, especially since you wouldn't expect to see organic fluctuations, is it worth investing in recoding a whole website from tables to divs? There are probably many better ways to spend that budget.
I would keep the site in tables until you are ready for a website redesign.. at which point you should make sure it uses divs.