I bought my SSD from crucial (from UK - took 2 weeks but no tax paid - they probably opened it up and couldnt be bothered - i did pay for season 7 24 from amazon uk tax so maybe they have a data base of how much import tax one pays and let people off!).
Anyhoo - i bought same time as the mac pro and never used the MP with the supplied 1tb boot drive - so havent been able to compare speed difference, however, comparing it to my 5200rpm mbp drive / load time, it is super quick - around 5-10 secs to boot up, apps open within 2 seconds, bar final cut, adobe apps (upto 10 secs - this IS NOT GOOD ENOUGH!😡)
The only thing you have to keep an eye on, is sometimes ive found Final cut writing render files and other apps writing to the boot when ive set the home directory on the 1tb stock drive - not really major issue (fcp needed its prefs trashed).
go for it - the great thing about having the mp, is that you can have a cheap ssd thats used for READING and a cheap 3.5 drive for WRITING / data etc..