Buy 802.11 N Airport Extreme?

[Emrtr4]

I currently have an 802.11 G airport with a 360 degree booster attached to a Netgear gaming gig router and am using an 802.11G airport express for WDS.
My wifi originates from my cable modem (cablevision, 30 megs down, 5 up) and on my second floor I am getting about 5 megs a second down and 1.5 up. I plan on buying a MBP with santa rosa later this year, but my question is whether I will see a huge difference with the 802.11N router.

I have heard great things about it, but I am not sure if it will provide me a huge improvment given that I am going through two concrete walls (this will probably mean I will need two of them and have to run them in WDS, then will I still get the same performance in WDS?)

I want to run ITV on two televisions and I also have an Xbox 360 (and friends who bring over 360s and laptops sometimes) so I will probably end up running two networks, one at 802.11 N only and one at 802.11G only. So, is the 802.11N worth it or will I not see a great performance increase?
thanks

[munchmime]

and sort of confused, but I think it says
"And the AirPort Extreme is also Wi-Fi CERTIFIED to work with the 802.11a, 802.11b, and 802.11g wireless standards — which means the systems you’re already using will work seamlessly with the new base station."

so why run separately? and wouldn't the 802.11n see the 802.11g's and work on that network anyhow? Also what type of concrete walls? or are they cinder block? lastly why not, if you have to, get a masonary bit, drill a hole and use an ethernet cable to bridge 2 of them together or just bypass the room to eliminate the possible interference? would that just not be cheaper anyhow? Bits are cheap, and cable is cheaper than putting routers in place?

[Emrtr4]

I wish I could drill through, but that is not a viable solution. Also I do not want to run a 802.11N/G network because on my G network now I know that if I run a G/B network it drastically slows performance and I assume the same will stand true if I run an 802.11N/G network.

[AndrewS]

Emrtr4

Actually - 802.11n was designed so that 802.11g and 802.11n can coexist and run at their own speeds - no speed hit for either g or n running an 802.11g device on an 802.11n network.

There are 3 antennas inside the Airport Extreme one for b, one for g and one for n.

Mixed networks are a speed issue with an 802.11g but not with the 802.11n standard...