If you need a NY spring setup, I think a NY olive and the standard 5lb connector combo is best. This is in conjunction with a standard fit/polish Glock trigger tune-up. Nothing major just slicking up the stock parts to remove the extra friction caused by the semi-rough stamped/machined Glock parts.
The trigger pull with a NY olive spring and either the 5lb or 3.5lb connector is going to be HEAVY. The 3.5lb connector helps a little on the break weight but I don't think it's enough to make it worth the extra $20 when paired with a NY spring. Save the 3.5lb connectors for guys who want a lighter "competition" trigger.