An important little thing to note about dissasembling higher tech items to boost your tech is that any 1 item dissasembled will give you approximately 1/40th of the points needed to get to the next tech. If you are more than 1 tech behind and you want to get the maximum benifit from the salvaged item then you need to first upgrade your tech untill you are 1 tech behind that of the item. An example would be if you salvaged a bunch of 25cm V5/C5 railguns. If your current tech is 15cm V3/C3 then you would want to upgrade to the 20cm V4/C4. Using numbers that are just memory the 20cm V4/C4 needs about 8,000rp for each part while the 25cm V5/C5 needs 15,000rp for the corresponding tech levels. If you get 1/40th of the points you need then this would be 200 points vs 350 points.
A couple of points about dissasembling items. Make sure you do not have any of the relevent tech being researched, or in a research que. After each time you get a message that you have successfully finished a tech make sure you do at least 1 5 second turn before continuing. Also make a copy of the database before starting to dissasemble the items. These things will prevent a major bug normally, or at least allow you to recover without having lost a lot of time. The bug invovled will occasionally completely delete the colony at which the items are being dissassembled. THIS IS A MAJOR PROBLEM. That you probably do not want to have to deal with.
Brian