As above some very valid points and more besides.
Against the Rs.
Most of the £1k lumps have done over 100k miles. Cost of a water pump. And it's still not a forged engine.
For me, I have a garage full of zetec bits including a new head. New sump and lots of bits and bobs.
Buy a bad st and you loose £100~£300. Buy a bad rs lump and it would upset me some what more.