iPhone 4s wifi slow.

Purchased the phone on launch day had sluggish wifi issue from straight out the box incidently the misses has an iPhone 4 and all was well upuntil the ios5 install now she has suffered the same sluggish wifi speeds (just under 1mbps ive speed tested on my laptop and am getting 9mbs consistently) instead of running straight to the forums i thought id try and look into the issue via forum reading etc seems the problem was apparent in the 4 as well.

Ive tried every possible remedy i could find, restoring, wiping network settings, changing the dns settings, changing my router to 'b' only the only thing i have not tried is a different router as the one im using (Netgear WGR614v6) doesnt have the ability to use the mode 'N' and have read that could remedy it or wireless connection but with numerous other devices connected without problem i cant see how it would be a factor especially seeing as my partners iPhone 4 is experiencing the same issue after the os upgrade.

If anyone has the same issue or could perhaps point me in another direction i would be very greatful.