SLVR is quad-band, although you are in UK, so unless you travel to North America, that isn't an issue.
L6 screen is CSTN 65k colours, L7 screen is TFT 256k colours
L7 has better battery life.
http://www.gsmarena.com/compare.php3?idPhone2=1053&idPhone1=1118
The SLVR is by far a better phone...