I'm not sure why you're separating Silk Road from other people who pay for goods and services
.............another larger portion by Silk Road, and the rest (people actually paying for their goods/services) would be a very small portion. Like a hand full of transactions.
Like it or not Silk Road is a huge part of the Bitcoin economy and it's going to stay that way until drugs become legal or go out of fashion. Have a look on the Silk Road forums if you want to estimate the amount of business they are doing.