Re-wiring

Hi all,
I've decided that its time to re-wire the archaic phone setup in my house and I thought I might as well 'pimp my wiring' in the process.

My signal box splits the signal form the BT wire to a master socket (ADSL / phone) and an extension socket (phone).

My master socket will require about 8m of cable from the signal box and the extension about 15.

Firstly, I was wondering whether I should keep this setup or have a dedicated, filtered master socket and daisy-chain the extension from this.

Secondly, I was wondering whether I can use a higher-grade cable than the standard cw1308 - such as solid-core speaker cable (I only need 2 wires after all) or CAT6, and would it be worthwhile?

If I can nock off a couple

Firstly, anythging before the master socket is BT's and you should not alter, change or move it. End of warning.
There is little point using anything `better' than CW1308 spec for such a short run, its unlikely to make any difference. Do not use speaker cable or alarm cable, stick to twisted pair CW1308 or CAT 5 solid core if you must.
A filtered master is only thing likely to make much, if any,difference.
If you connect dirrectly to the test socket with the extension and everything else disconnected and there is no difference, then any changes are likely to be futile.

If your extension socket is the one with the ADSL modem on it, then the best course of action is to get a good quality filtered master socket (like the XTE-2005 from ADSL Nation) and connect the ADSL modem to that, and then run Cat5 back to the PC. If the 15m extension is just for the phone, then just fit a filtered master socket. Don't fiddle with anything before the master socket - if/when BT find it, they will re-wire it at your expense.