Ok peeps mind made up ill wait for another build or when it comes out officially till then I will leave the post open to other members thinking about doing the same, once again windows central family thank you for your help
I did a clean install to W10TP on my 640 and it was very laggy, even more so than 10166 Imo. W10 does look visually better than 8.1, just not near as smooth. I will try out next preview build when it comes out, but 8.1 way more stable and fluid.