Estimating new route time/fuel burn
If your routes are in Europe and your quote is for some time ahead it would not be possible to predict the exact route which would be available. As you know the RAD changes every 28 days. The best that you can do is to run a flight plan on the current routing with, if you have the option, statistical weather for the month or quarter that you are interested in. This should be close enough in terms of fuel burn and time.