Raymo I based that comment on plugging
assumed 8" newt figures into "Newt for the Web" design software:
http://stellafane.org/tm/newt-web/newt-web.html
I don't know which 8" newt you have so I can't comment on the secondary size exactly. Contrast is (relatively) affected more than light gathering is according to the performance notes on Newt Design.