Found this natty little TODC/LDC calculator for the Q400, available at:
http://todc.sas.dk/todc/index.htm (http://todc.sas.dk/todc/index.htm)
There's also this V-speed calculator available to download, which looks at your current aircraft weight in FSX and then sets the bugs in the Majestic Q400 accordingly.
https://dl.dropboxusercontent.com/u/53870244/Q400VSpeeds.rar