Bloody hell!...you lot and cut springs
It's dangerous, will fail an MOT and will ruin OEM dampers....let alone give you completely S*!t ride quality and bog all handling! And if you were in an accident it will probably invalidate your insurance.
As for cheap coilover sleeves....they are ok as a temporary solution, but if they are to be put on an OEM damper...the firmer spring rate will knacker the valving and kill your damper. This is also true of cut springs....hence why EFinlow has got issues. As for the Ebay sleeves...the spring rates are anybodys guess....and will almost be certainly of uniform rates....rather than having a front/rear set of spring rates.
If you want to go really low, then you need a quality damper and coilover-sleeve (like a Koni and Ground Control combo) or just get some proper full blown coilovers....K-sport, D2, MeisterR, Teins...etc.
As for spring/damper combo's, as above although there is also Tokico and Gaz that are well recomended.