I need your advice about my keyword research

Hi guys,

I am newbie but I follow this forum for a couple of months and I have learnt many things. I have read most of your comments about how to find a good keyword research tool. Many of you recommend the Google Keyword tool which is free and many others are fan of Market Samurai tool, Niche Finder or other tool.

I am currently using the free trial of Market Samurai tool and I find that it is extremely slow and that quite a few times makes my mac stuck.

On the other hand I have read many blogs such as Pat's or Tyron's blogs and I have some questions about how to analyze correctly a keyword with the use of Market Samurai in order to build a niche site.

I am trying to find a niche in the French market (french language and so french keyword). I have found some keywords with
- SEOT around 112
- PBR between 1%-3%
-SEOCompetition less than 30.000
I have also checked the average PR of the 10 first sites in Google and it is about 2 (the average).

Here after my questions:
What is the importance of the Phrase to Broad Ratio (PBR) factor?
What limit do you put on that factor? Some bloggers advice a 15%.
What do you think about that keyword? Is that a good one?

I did the exercise using broad match and not exact match.
Is that the proper way or I need to research with exact match?

Finally I would like to inform you that I have also checked the keyword with the Google Keyword Tool. It has a big number of monthly research
Broad monthly researches: 8100
Exact monthly researches: 170

and when I put the keyword in quotes and search it in the Google I find about 44800 results.

Could you please help out to understand what is the conclusion of all that. Does the keyword is a good one or not and why?

Thank you very much in advanced. I appreciate your help!