The connection speed you are talking about is the wireless connection speed between your PCs wireless card and the router itself. Each router will have differing signal strengths so it could be that the AOL supplied router just has a weaker output than one supplied by Orange. To check how good the wireless link is, move the PC so that its next to the router, see if that gives you a constant 54Mbps connection that is stable. Also test your youtube connection from there.
If it resolves your problem you need to eliminate the cause of the wireless connnectivity problem, if not then you need to look at the broadband link.
However, all that said if your Internet link is slower than the the speed of your wireless connection it is unlikely that the problem is with the wireless link e.g. if you have 2Mbps adsl and you are getting 5.5Mbps wireless connectivity to your router then that is twice as fast as the Internet link so if you constantly have buffering of live feeds it may be your Internet link or even the website.
I have a constant 54Mbps wireless connection and a 2Mbps cable link and on occasions I get buffering on youtube, it may just be the number of users on youtube. If you do go for a new router please be aware that on AOL you must change the MTU size set on the router. http://myaolbroadband.co.uk/broadband/faqHomeNetworking.adp This link takes you to the page and it states that you must set the router or your PC to an MTU size of 1450. Just check what the speedtouch is set to.
Hope that helps! Reg99