Thanks Rowleybob...will def. bear that in mind. I read an article about it and it also mentioned the clip brush as well. However, the only major difference I could understand was, apart from better peformance (which is always the better option!), was that the clip brush would allow the player to shoot through the brush...so for example, if i were using the tool_box.mdl and the player decided to shoot at it, it would not appear solid, (ie. no sparks from the bullet) whereas using the invisible {blue texture you can shoot it. Although this might not be a justifiable cause to use the {blue texture in all cases, I think it is good for some.
However, another downside to this is that obviously, shooting the toolbox does not produce the sound that would normally occur from shooting a metal texture.