yes 
you can load os 5.0 on 8330 if the website says so  
i loaded os 5 on a bb 9530 also  
all os 5 is available to 8330 and 9530 , only to poeple who have bis 
you can load os 5.0 by using forced loading method 
well for that what u need to do is  
-install os 5.0 
- then download and instal bb desktop manager 4.7 or older 
try using as old bb usb drivers as possible , new drivers wont allow u to use this 
i use the bb drivers of mfi tool which work perfect ( in case anyone needs i can upload it ) 
- then remove battery from curve 
- open app loader and delete vendor xml file ans start app loader 
- connect device to pc it will show pin now reinsert battery , and in some time it will show "unkown" in place of pin no , at this time just press next , remember timing is very important , press next as soon as u see unkown 
then it will show you os 5.0 and ask if u want to update  
unless you do this it will not show you os 5.0 even if u use app loader as per post 1 
you have to force bb to take os 5