right ditching the lob and sand wedge for a 57 degree smt sand and keeping the 52 degree, which leaves space for a rescue of some description basically a club which will be able to go further than a three iron as the difference between the three and the four is neglible... 19 degree then?

will have

driver 3 or 4 wood
2 iron
rescue which loft ?

4-pw, gw, sw

I would go for a 22 degree - this would be equivalent to a 3 iron or 7 wood.

I carry 4W, 7W, have thrown out the 3 & 4 irons.

My rescue is a 25 degree to replace the 4 iron.

Carry 4 wedges, 47, 52, 56, 60.

20-22 degree sounds like it but i wouldnt advise mixing and matching irons and rescues. as you have a two iron in your bag it may also be an idea to have something to mix and match with it - a 7 wood for example. but i would recomend the following line up based on the clubs you already have, you are thinking about getting and the ones i would recomend
driver
4 wood
7 wood
23* hybrid
4-pw,gw,s/lw