I haven't yet I'm afraid! I've tried this:
"Netgear N600 Wireless Dual Band Gigabit ADSL2+ Modem Router" http://www.amazon.co.uk/gp/product/B004TR5HF8/ref=oh...
but this doesn't support fixed IPs
I then tried just a router/wifi box to link into the existing modem "TP-Link TL-WDR3600 N600 Wireless Dual Band Gigabit Cable Router" http://www.amazon.co.uk/gp/product/B008QBAXI4/ref=oh...
and again this doesn't support fixed IPs.
I've just tried a separate wifi access point "Linksys WAP300N Wireless N Access Point" http://www.amazon.co.uk/gp/product/B00BMPB4QG/ref=oh...
but this only supports either 2.4Ghz or 5Ghz not both at the same time so I'm back to square one again.
I've looked at the ZyXEL SBG3300-N but this doesn't appear to support the new dual band wifi.
DrayTek Vigor 2830n-Plus does support the dual band but it is £209 so I'd rather find something a little cheaper.
To clarify I'm looking for an ADSL2 modem/router with dual band wifi that supports fixed IPs.