Worsted Weight Yarns

I have a gripe about medium/#4/worsted weight yarns: not all of them knit up the same way with the same needles. The reason I am having this trouble is because not one brand of yarn has all the colours I would like to use for my friend's afghan. Therefore, I have decided to make it a little bit like a "crazy quilt" and really go with some really different size "blocks" (rectangles etc.). One of the new items will be a long "stripe" that will use the DNA pattern I found on the internet. This is the URL www.twosheep.com/helix/ Of course, I am going to have to come up with an interesting way to put all of this together. Any ideas?