the 4500u(1.8ghz with 3.0ghz turbo)... 4510u(2.0ghz with 3.1ghz turbo). the difference in minimal and would never be noticed.
4gb vs 2gb... their both ddr3 which is slow compared to even 1gb of ddr5. i cannot understand why so many laptops have 2gb or more vram when these graphics card are nowhere near powerful enough to use 2gb vram. i guess for some non gaming work like photoshop or render this could come into play... but for gaming there is no advantage.
the dell is just as good and will provide decent 720p(1366x768 common laptop resolution) performance in games... but dont expect any modern games to play at 1080p.