speed difference priority traffic vs non priority

[#1]

I'm currently on BBYW Pro but am finding sticking within my usage allowance is getting difficult so was thinking on changing to Option 3.
It seems the main difference between the options (other than usage allowance) is that Pro traffic is given priority.  What does this actually mean speed wise though.  Is there a noticeable speed difference.

[#2]

Have a look here as a first shot http://www.plus.net/support/broadband/quality_broadband/speed.shtml?link_bbyw_view1=speeds#Option3sp...

[#3]

It really depends on what you're using your internet connection for.
Have a look at the link that Jim posted and feel free to ask any more questions if you have some.

[#4]

Thanks for the link.  I was looking for that earlier but couldn't seem to find it.
Anyway I think I will be better switching.  I need the bandwidth more than the speed