Thanks blackshadow for your reply. I am using the tronkyfran theme, and the raspberry Pi 3b standard. My plan was to make the boxart at a high res, cause I am using the boxart as the screensaver.

I scraped again one full gamelist, at 1200 x 768 and that worked very well in the game list, no lag, and the screensaver boxart now doesn't look stretched or pixilated at full screen.

Hope this might help someone in future, if they planning to use boxart as the screensaver.

Thanks blackshadow all the best