Puzzle me this....
Thanks Old Smokey. In the interim I have had some good fortune in answering my own question.
As I previously mentioned our operation has the luxury of not having to operate at high gross weights, so the solution we were looking for was based around balanced field and minimum V1's, as opposed to trying to extract high take off weights and the resultant higher V1, and in some instances unbalanced fields. The drop down options in the BLT allow the user/airline to determine what V1 policy they wish to adopt, taking into account the above. Operating costs, vis-a-vis the use of reduced thrust or derates, will also be affected by the take off policy. The IATA manual (which I was fortunate enough to get a copy of in my hour of need) sets out the standard options that aircraft manufacturers will make available in their standard computerized take off performance. It turns out our best option is a balanced V1 which will also equate to the closest speeds to the FMC (which only looks at the runway itself). This is useful to us as it is a good cross check that we've done it right!
For what its worth we operate 737-700's.
For those who still use paper performance, the advantages of a system such as the BLT - if used correctly, which is what I'm trying to achieve - is enormous as it gives a great deal of flexibility and is alot less restrictive particularly when operating with DDG items or on short/contaminated runways.
Hope this helps the performance minded out there!!
Happy take offs!