Is a 2.8GHz processor recommended instead of a 2.3GHz?

The best way to see the differences between the different logic boards that would work in your system is to use EveryMac web site. Its a bit of work but its a very useful tool! Here’s what it can show you between the early and late 2011 systems (same hardware across)

13” MacBook Pro 2.3GHz vs 2.4GHz Core i5 CPU’s as we can see there is a bit of difference I doubt you notice the differences between these two Core i5 systems as hard as you try. Now lets look at comparing the i5 2.3 vs the 2.7GHz & 2.8GHz Core i7

So its clear there is a more sizable performance improvement between the i5 & i7 chips but between the early and late i7 not as much! So does it make sense jumping to an i7 vs the i5 you have now?

What you are doing with your system has a large bearing here! Writing, reading web pages looking at your pictures or even watching vids I doubt you’ll notice any differences. If you are working on large data sets object graphics, composing music, working on video production then you’ll likely shave minutes in your work flow.

To be honest, the Intel 13” models only use the Intel graphics engine whereas the 15” models offer a discreet GPU so anything graphically oriented will perform much better than the 13” model running the same CPU!