SEO peer review - good or could do better?

I have been learning SEO since about October last year, and at that point our Accountancy website was on about page 10+ of Google results for keywords.

I spent 3 months optimizing the on-page SEO of the site (part-time as this is not my day job), and also added a blog section and social share buttons to the site. New quality blogs every 3 or 4 days. Added Facebook and Google+ sites. Plugged everything into Google/Bing webmasters, and Google Analytics.

Since Christmas I started on back-linking. Mostly directory (targeting about 5 keyword phrases), some commenting on other blogs - no reciprocal or paid links.

Anyway, at Christmas to keep track of the directories submission I also started recording SERPs stats in Excel. These are the results to date across 12 generic keyword phrases (pretty much every possibility to find a local accountant), none including our company name:

27-Dec-11 | Average SERPs 7.62 | Google external links 1006 | best keywords position #2
13-Jan-12 | Average SERPs 7.15 | Google external links 1867 | best keywords position #2
14-Jan-12 | Average SERPs 5.08 | Google external links 1867 | 2 keywords at position #1
17-Jan-12 | Average SERPs 4.23 | Google external links 1867 | 3 keywords at position #1, 3 keywords at position #2 ie. top 6 keywords all in top 2.

So given the jump after the 13th (and ongoing) and the number of Google registered back-links not changing, what do you think has caused this jump, me or Google itself?

The competition is a few hundred other accountants in our city/area with the highest competitor mozRank only 5 (we are currently at 4 but that may be a little out of date). So what do you think, is this good progress or would a big SEO company do a lot better?

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