Honestly chrome has become so heavy that I cannot imagine new tab opening with hq image.
Not commenting on your plugin.
Not commenting on your plugin.
I did not notice any typing / suggest box lagging or performance problems and I do not have the strongest laptop. The same thing for some extensions that I used before and rendered background image.
AFAIK these things should also run in separate thread, so lag in the web page should not freeze omnibox.