rsq219,
I would not recommend the 243 WSSM. I have heard nothing but bad things about this chambering. However, I think the reason for it's lack of success has to do with the brass. If Lupa or Norma made brass for the 243 WSSM, it might be performing better.
It sounds like you are wanting a high velocity 6mm. If I were you, I would buy a Krieger 30" barrel and have it chambered for the 6x284. The 243 AI and 6MM AI are awesome performers too, however, you have to fireform form those two chamberings. The 6x284 only requires you to neck down a 6.5x284 case to 6mm, it's very easy. A 6x284, with a 1-12 twist 30" barrel, will push a 75grn V-Max at 3900 to 4000fps and the 87grn V-Max at 3700 to 3750fps. The 6x284 will push the 105grn VLD bullets at 3400 to 3500fps. If you want to shoot the VLD bullets like the Lupa 105 Scenar, Hornady 105 A-Max and Sierria 105 SMK, a 1-8 or 1-8.5 twist barrel will allow these bullets to perform well. However, if you go with a 1-10 twist barrel you will be able to shoot the 75 V-Max and 87rn V-Max as well as the 105grn VLD bullets too.
I know guys who have tried the 243 WSSM and they all have rebarreled their rifles for either the 6x284, 243 AI and 6MM AI. They all said the 243 WSSM chambering has great potential if the brass problem can be solved. But until that happens, they all said they would NOT recommend the the 243 WSSM.
Also in order for you to change to a 243 WSSM, you are going to have to make many changes. If you go with the 6x284, 243 AI, 6MM AI, you will not have to make changes to the bolt face, so it would probably be cheaper to buy a barrel and have it chambered for the cartridges I have mentioned.
Good luck with your choice.
Wildcat