I doubt if it would make all that much difference using Skype bandwidth wise.
Why not download the Tautology Bandwidth Meter free from:
Very small file, very easy to install and gives you full details of bandwidth use currently, daily and monthly.
By the way TalkTalk's Talk3International gives you free phone calls AnyTime in the UK, plus 28 other countries including the States, Australia, Canada, and Europe, plus low rates to other countries..:-)
Plus free broadband although you wouldn't necessarily have to change ISP.
Broadband connection is taking some time at present due to sheer demand, but the phone service switch over is about three weeks.
You now have to ask for the full international version at £9.99 as the £8.99 only includes UK calls.