Clock speed ('Ghz') is not all that matters when it comes to performance.
Quite a few things can dictate how well a certain CPU performs, including but not limited to
- IPC (instructions per cycle)
- Arcithecture ('nm')
- Clock speed ('Ghz')
- Cache ('MB' & 'KB')
- Cores (1,2,4,6,8,etc.) (multi thread performance)
- TDP ('W','Watts') (Power consumption)
Furthermore, a CPU's desirability can furthermore be increased/decreased by how many features it has and what chipset it uses.
- Hyperthreading (Virtual cores)
- RAM capacity
- RAM channels (Complicated stuff, not too much to worry about)
- Chipset (Does it support modern motherboards?)
- Integrated graphics (does not require a separate graphics card)
- Pentium 4 2.8Ghz
- i3 uses 22nm architecture, P4 uses 120nm
- i3 has a 15W TDP, P4 has a 65W TDP
- i3 has integrated graphics
- i3 has hyperthreading
- i3 has 2 cores, P4 has 1 core
- i3 has a newer chipset
- i3 has a built in memory controller
- i3 has more cache
- i3 has a variety of features the P4 doesn't
(i3 on the left, P4 on the right)
(Higher is better!)
- Passmark | 2435 | 325 | i3-4005U is 650% better.
Unfortunately there are no other benchmarks that I can find that contain information on both the i3-4005U and the Pentium 4 since the Pentium 4 is 11 years older than the i3.
Get the i3-4005U because it is far less outdated, requires no dedicated graphics card, uses a less outdated chipset, and performs much better in terms of single core performance and (because it has a second core) dual core performance.