My transition from a 2009 Ninja 250 to the 2012 BMW s1000rr was no problem (other than the height of the BMW had to be lowered for me a bit and the suspension needed to be set up for my size). Before I bought my own BMW, the first 5 experiences I had on the s1000rr were with California Superbike School where I could gradually get familiar with what the bike was capable of doing in a safe environment (track) while also learning to be a better rider. Considering your Ninja 300 already has a slipper clutch and ABS brakes (just like the s1000rr), I predict you'll have an even easier transition than I did!
Do, or do not... There is no try.
'09 Kawi Ninja 250 CVMA #717
'12 BMW s1000rr
I like extremes.