Benchmarking is about comparing two systems with exact same settings.
So the answer "is the old 1600x900 laptop faster or slower than the new at 1920x1080" needs to be answered by running the benchmark on both systems at same settings. That's what the default settings are for.
Note that 3DMark Vantage scales the benched resolution to screen resolution - so if you want to compare at 1920x1080, you can run at that resolution on both systems. The 1600x900 one will just scale it to the screen.
Running at two different resolutions would be like tractor pulling with ten ton load against another with 20 ton load. You might be surprised to find out that the one with 10 ton load will do better... even if there are differences in the tractors themselves...