Would I notice changing from a 6 deg stem to a 0 deg rise stem?

Only if it was 300mm long. 🙂

Nah.

turn it over and get a 12 degree then put a 5mm collar in then prob will be about the same and then you can compare?

Edit: duh or even just take a 5mm collar out and would give you the same effect I would think? 😳

Sorry, should have said: It's for a 70mm stem.

you wouldnt really notice it IMHO –

Probably drop you bars by about 7 – 7.5mm (if my maths is correct). Depends if that's what you want – it might feel a bit different but probably not.

Yeah it's about 7mm (I worked it out in AutoCAD). I have just remembered that I took the spacers out that were below the stem so if I find it too low, I can always put them back in.

I'd say maybe… in terms of handling prob not, but…

On my full susser, if I remove one 10mm spacer from the bottom and put it on top of the stem, I get the most god awful backache after about 2 hours which doesn't materialise with the spacer back in place.