Pentium G620 is a Sandy Bridge CPU. Sandy bridge is the microarchitecture or design of the processor core.
I am assuming you mean the i3, i5 and i7
going from lowest to highest
Celeron is the lowest with mostly a single core (some model got 2) and most thing disabled.
Pentium has two core, higher speed, but lacks quicksync
i3 are dual core with quicksync which accelerate video playback.
i5 got 4 core, "K" version has unlocked multiplier
i7 adds hyperthread
sandybridge-E adds 2 extra core but uses different chipset/motherboards.
The G620 is a sandybridge CPU. Sandybridge is the architecture/generation of a set of CPU's ranging from the g620 and including the i3 2100, 2120, i5 2400, 2500, 2500k, i7 2600k (and others).
The G620 is a very basic duel core model however with a basic gaming card it would likely be better for FSX than the AMD's you listed in the other thread. The ideal budget sandybridge though is the i3 2100 and the top dog when budget doesnt matter (for gaming) is the 2500k.
In the coming days Intel will release the next generation of CPU "Ivybridge"
G620 may suit you well as when combined with a decent motherboard you have the basis of a system with a good upgrade path at a later date when budget allows you could drop in an i5.
If you can stretch the i3 would be better than the g620.