There is no miminum income required to sponsor your spouse, but they want to see how you will be support yourselves without relying on welfare. That's why they ask about the sponsor's employment history and income.
Do not rely on the wait times posted on CIC's website, for a few reasons. First of all, they are not averages; they represent the amount of time it took for 80% of applicants to get through. If 79% of people are approved in 3 months, but next 1% took 4 years, the site will show 4 years. It's really not a useful guide. Secondly, you don't know what visa office will handle your file. It could reasonably be London, but it could be Ottawa. Thirdly, the UK office is skewed because they recently absorbed some work from Pakistan.
Have a look on this forum for a thread called something like "UK applicants" and you'll get a much better sense of real world times. I personally believe there's a chance you could get approved prior to November, but it could certainly go longer.
The major concern for couples that aren't in Canada is proving to the CIC that they intend to return to Canada. Where will you live? Do you have a job lined up? etc etc etc
The other thing you have to worry about, given that you're applying common-law, is proving that you've lived together as a couple all this time. Lease in both names, mail addressed to both, utilities in each other's names, joint bank accounts, life insurance with the other as beneficiaries, etc etc etc.
Of course if you get married now, you'll have much less burden of proof required for your marriage and you'll get the application much earlier and for sure you'll be approved well before November 2016.
