One of the great things about Lightroom is the fact that you can run multiple exports at the same time and it doesn’t seem to strain the system too much either. I sell my stock images through 3 particular outlets – Alamy, Photoshelter and Fotolibra.
Alamy require Jpegs that are up-sized to 48MB (when uncompressed) or over. Fotolibra don’t mind too much but they prefer TIFF at 48MB. Photoshelter is a different matter, as I use their system to drive my on-line galleries and direct sales, so I don’t need to upload up-sized files, the originals are fine.
So with this in mind I have set up Lightroom with at least 3 main export presets (I do have others for other purposes) that cater for Alamy, Photoshelter and Fotolibra accordingly. You can use LR to up-size images and it seems to do a very good job although I am not totally sure how it does it, my guess is that it uses the bi-cubic method.
The brilliant thing is that I can run all three exports at the same time, leave the PC to chew on it and then come back in a little while to find 3 folders stuffed with the freshly exported files which can then be sent to their respective destinations!