Well, it depends rob21. Many people applying through Buffalo have their entire applications determined in less than the 8-9 months it takes to get through the first stage of inland applications.
My case was slower than most, but if we had not made a mistake with a document (now we're just waiting about a zillion years for a govt office to get another one for us), we would have had PR in mid-October, or six months for the whole thing from start to finish.
Another thing to consider is that if you are rejected inland there is no right to appeal.
How did she obtain an open work permit? Did she graduate from a Canadian post-secondary institution after April 2008? Very few people are eligible for open work permits.
If you apply through Buffalo she will still have implied status while her work permit renewal is considered. Whether you apply outland or inland, you will need to submit a renewal application to Vegreville before the permit expires. We did this with my spouse, but in our case we extended the visa and changed it from work permit to visitor. I don't think where your sponsorship application is being processed would have any bearing on whether it is renewed.
Renewing the permit she already has is a different issue from the application for an open work permit that most people include in their inland applications. You are going to need to apply for an extension of her permit whether you go inland or outland. Just submitting a PR application inland will NOT give your spouse implied status on her current work permit.