I am currently an Xnet customer on River torrent plan. Currently getting a line speed of 1.0Mbps downstream. (1.2Mbps attainable speed.)

This may be a long story:
I was with Xtra 2 years ago on a 10gb plan, forgot the actual plan speed, but i was getting ~1.8Mbps. When the Xtra Go Large plan was out i was automatically transferred over to that plan, the day i got the plan, my linespeed dropped down to 0.8Mbps and i guess it was understandable because of the large amount of people on that plan. However i later discovered that 4 of my other friends were able to get full adsl speed 7.6Mbps on the Go Large plan and i assume that they're living close to the exchange. But another friend of mine living 3 houses away from me was able to get 2.5Mbps, now i really don't understand how that is possible since we're both connected to the same exchange and on the same plan. I then rang Xtra to ask for an explanation, but the only answer i got is "the connection speed on the Go Large plan is not stable, it would be better if you change to another plan and that every house connection to an exchange is different, even for neighbours." The most frustrating thing is that i cannot believe someone would say "i don't know why you are complaining, 0.8 megabit is still quite a good speed." I'll assume that no matter what i say, Xtra would not provide any useful customer service unless i change my plan.

I then changed over to Xnet, the plan i'm on now.
As expected my line speed stayed the same @ 0.8Mbps. I then rang the helpdesk, they then told me to do a series of tests to see if it's a problem in the setup within my house and the results showed that it's not. They then contacted telecom (Chorus) to see if there's a fault in my line. A technician came to investigate the next day and told me that he's getting ~1.9Mbps at exchange and ~1.7Mbps outside my house and ~1.2Mbps inside my house. He said the cause of this might be moisture build-up along the telephone line or having too many phonejacks in the house. He then asked about my modem (brand and age), it was a Billion and i had it for 2 years, he then suggested that my modem's too old and that i should get a Dlink modem. I did, and i'm getting a speed of 1.0Mbps however, the line attenuation seemed to have increased from 39dB on the Billion to 47dB on the Dlink.

My questions:
-How come i had a "attainable" line speed of 1.8+Mbps 2 years ago which has now dropped down to 1.2Mbps? (moisture build-up?)
-How come my friend 3 houses away is able to get ~2.5Mbps even though we're probably connected to the same exchange?
-I'm still using the same ph. no. as i was 4 years ago in my old house, would that make any difference?
-Most importantly, is it possible to get a better line speed?

Things i've tried:
Changing all the cables, changed my modem twice, changed isp and anything thats possible under my control other than moving house.

Note: The staff at the Xnet technical support were very helpful, best i've seen so far. Keep up the good work!