You gain more exp on each individual toon by having more people in a group when power leveling with an 80(/70/high level character) in group, so you may as well level all 4 to 60. I haven't personally verified if this is true since 3.0, but it's not like Sam tested his theory either. Aside from the added costs of doing this compared to a more standard approach this is the only reason to not use this method.

You can grant 30 levels from one character. I have personally done this using my own raf and it is said in the official faq.
I have also read that you can grant from gifted levels, but I haven't verified this either personally or with an official source.
Aside from the few gifted levels from A to original, is there any reason they need to be linked?
When you transfer a toon you lose all of the levels they could have granted. This is from the official faq. There isn't any problem with this, I just thought I'd mention it in case someone was wondering.

I have 1 day 3 hours and change on my first attempt at boosting to 60 with raf, and this was not even close to an ideal method. Mercurio's 16 hours looks like a good time to try to beat if you want to try to start saying questing is faster than boosting, but then again this was with a 70 and it might be less now.

Information doesn't change based on who it's from. Sam may be horrible at leveling but that doesn't change whether his advice on the subject is good or bad.