Lookup field to a list with 65000 items

Hello,

A list <A> will have a lookup field to a list <B> with 65,000 items. I also want to use OOTB functionality to insert/update the items in list <A>. The list <B> should grow about 200 items/year.  What should be the best approach?

My approach is to add a web part to the insert/edit form that would filter the items from B and somehow "inject" the selected value to the appropriate field.

Another approach is to use external content type and store the values to an SQL server - list B should use external content type. The web part should read the values from SQL server and the user will add/update values using OOTB Sharepoint functionality

Thank you

Christos