DSF

I have bought hd metal but it is about 2mm bigger than the printable area, just wondering does the Ricoh print borderless?

Nope - nor would it do you much good, as you still need an area of blank, unprinted space around the design to run your heat tape off on to.

You may have already done this, but apparently the Ricoh do not print their maximum area as default, wont offer borderless by may give you the 2mm you need

https://www.youtube.com/watch?v=q5eh44auY0E

it would mess up your machine doing full width as some would spill over and ink up the paper path

Yes, you can certainly go a little bigger (if you are using the SG7100DN) by buying the bypass add-on which allows up to A3+ size:
http://www.printerowners.co.uk/sublimat ... s-tray.htm

Does anyone know if there's at least a way to view where the print will cut off on print preview so you know how much you need to shrink it by?

Try set paper to letter and than print