If I have a very close STR Marker match, does that mean we are closely related?
It may, but not necessarily. Persons with the same terminal SNP are more closely related than those with a different terminal SNP, even if you have a close STR marker match to someone with another terminal SNP.
Why should I consider a Big-Y Test?
The Big-Y test for a R-L226 man will check all the terminal SNPs for the Cluster AND provide you with a list of 'private' SNPs, those that have occurred in your ancestral line since your line left the R-L226 Tree. As others test Big-Y, you may find that another person may share one or several of your 'private' SNPs, and so define a further branch in the tree.
Should I order the R1b - L226 SNP Pack to learn more about my terminal SNP?
If you have taken the Big-Y test, then NO, all the SNPs in the R1b-L226 SNP Pack have been tested for you in Big-Y.
If you have NOT tested Big-Y then YES, the R1b - L226 SNP Pack is a very economical way to find your terminal SNP. It will not reveal your 'private' SNPs however.