Re: Lapua, up or down? 260 Rem
"I have the Lee Collet die set for the 260 and I don't know if I can use that to resize."
KRP is correct.
NO neck die is useful in reforming, IMHO. The otherwise EXCELLANT Lee collet neck die would be the absolute WORST choice for any reforming! You will need a FL die to complete the 260 case reforming to make the neck-to-sholder junction right so get one, there's no real option on that in my mind.
And, if you also have/get a 7-08 FL die for an intermediate step, you can use it for a "body die" later. Just use the Lee 260 neck sizer to finish sizing. Together, those two dies will help you make the straightest possible 260 cases, which is the first step in getting great concentricity of your loaded rounds.