Any way to improve xbox live lag?

[elitetrick]

Im on zen 8mb with these stats
ADSL Link Downstream Upstream
Connection Speed 8128 kbps 448 kbps
Line Attenuation 14 db 3.5 db
Noise Margin 12 db 23 db

download speeds on websites and torrents is very good and playing cs i get ~20-25 ping and it works fine.
but when it comes to playing halo3 on xbox live half the bullets dont register.
for example it takes 4 shots to kill from a br but it will take me like 6 (no its not my aim). snipers kill in 1 headshot or 2 body but it takes me 2 heads / 3-4 bodies on average. on the playlist where its 1 headshot kills from a rifle it takes 2-3 headshots on average. i have watched back hundreds of games in theater to confirm that its not my aim.
as you can guess this in unbelievably frustrating so i was wondering whether theres any changes i can make to my router etc to improve this.
i have forwarded all the ports xbox apparently needs and my NAT is open.

my router is a Netgear DG834G v2. im playing on wired. UPnP is turned on with advertisement period 30mins and time to live 4 hops. MTU of 1500.

any help welcome.

if theres nothing i can do will switching to o2 20meg improve performance?? as this is an option.

 

[IdhDec]

From my experience it's the other players connection not yours. I know when i'm playing halo3 against people from america etc I am firing the sniper rifle into their head, melee, grenade etc and they still kill me. I don't really play it that much anymore but I get the same on GTA4: other cars "teleport" forwards and make me crash .