Power is only up by about 3 bhp and they've done that by adding 500 rpm at the limiter - presumably from the lighter valve train. 
I can't believe all that extra weight is in the exhaust system, so yes, losing it might be difficult.
Personally, (13.5 stone rider) I don't think the original forks need stiffer springs. They need revalving and some preload adjustment.
I had mine set up at a pro suspension shop and he said if he was rebuilding the forks he wouldn't change the springs because they were the correct weight. The rear shock, he said, was good in operation just some corners cut on the build quality. He wasn't impressed with the cheap looking preload adjuster ring.
I had my Ducati resprung with a factory Ohlins shock and a K-Tech fork revalve. Phenomenal difference. I think I'll do similar with the SDR when funds allow. Fit the race shock and have a revalve up front. 
I'm not even that fussed about lack of preload adjustment, because for me, mine doesn't need any more but I will lift the forks in the yokes by 5 mm to get a bit more loading on the front wheel. (The 2017 model has done that by ergonomic tweaks).