As I have a 29dB line (as reported by Tiscali equipment!) should I be able to get the full 16meg on Sky's Max Package?
Technically, but not as things currently stand!
As we have been saying for weeks - you have a line fault. You still have a line fault. You will continue to have the same fault if you move over to another ISP.
So at the moment, if you go to sky, you'll be lucky to get much over what you're currently on, and certainly I reckon nowhere near 8, or even 16Mb.
So it's either - persevere and get the line sorted now, or move ISPs and get the line sorted, and I don't know what Sky are like at dealing with line faults.