4.5 v's 4.5 LW

[A 7USC]

I'm being a little lazy by asking this on a forum, but this is a far more enlightening way to aquire information I find.

What's the difference between the two?

Has the LW now replaced the standard 4.5?

Which, in your opinion, is best to go for? taking into consideration that I would also look into a RR conversion after.

Thanks in advance for any info/thoughts.