The
G645 is based on
Sandy Bridge architecture while the
3855U is based on
Skylake.
Using the multithread performance as a reference, the G645 gets a score of
35.4 k points while the 3855U gets
24.6 k points.
Summarizing, the
G645 is
1.4 times faster than the
3855U. To get a proper comparison between both models, take a look to the data shown below.