Performance-wise, there are some big processor performance gains versus the 4800U:
Lenovo had a notebook featuring this part listed earlier this year. It is configured with an 8-core/16-thread CPU clocked at 1.80 GHz nominal, with up to 4.30 GHz boost, which may seem like a minor speed bump, until you compare its User Benchmark scores with those of the 4800U. Apparently, the 4900U has some boost algorithm secret sauce that makes it a double-digit percentage faster than the 4800U in multi-threaded tests (possibly better spread of boost clocks across multiple cores). The iGPU appears unchanged, with 8 "Vega" compute units (512 stream processors), and up to 1750 MHz engine clocks.
AMD Ryzen 9 4900U Graphics ????
— APISAK (@TUM_APISAK) April 5, 2020
FP6, 1 CPU, 8 cores, 16 threads
Base clock 1.8 GHz, turbo 2.35 GHz
AMD Ted3-RNhttps://t.co/Z7AYDtNip9 pic.twitter.com/Y9cvmSkF9N