what pipe for extra raditor

I wish to add an extra radiator in a lounge. Would it be ok extending from an existing radiator fed with 10mm plastic pipe, distance is about 6-8 metres to new radiator OR would it be better adding my T back from the 22mm pipe underneath the floorboard and run some 10mm or 15mm to the new radiator?
radiators are fairly big, adding same again:
milano vertical double radiator 1780x354mm 2256W