Hi Jochem,
Great to hear you are back into it and enjoying the Blast - a good board for people with the basic free ride skills and due to the narrower width, windsurfers who come back into the sport feel often more at home on this than the newer wider shapes of the Gecko which are great for intermediates.
Regarding the Jag/Blast- the Jag is a great Freerace board for higher speeds and mainly straight line sailing. The Blast 115 also good for straight line blasting but with more manoeuvre potential - so it depends a bit on the type of sailing you want to do - the sails you mention will tend to fit the Blast better/if you like the 130, you'll love the 115!