You can watch my full review of Reason 10.3 below. But the bottom line is that I saw a 130% performance boost using VSTs in Reason 10.3. I also got a 35% boost with regular rack extensions. No other new features were added to 10.3, but I'm just happy with the speed.
Thanks for being such a fan! Here's a free mini-refill for you to show my appreciation. This Refill should work on all versions of Reason after 5.0.
It includes 3 combinator synth patches - an 808, and evil lead, and a sweet pad. And some samples/loops to mess with.
Hope you enjoy!