GTX750Ti 2GB performance benchmarks for reference (see my comment on 750Ti vs 750):
http://www.techpowerup.com/reviews/ASUS/GTX_750_Ti_OC/25.html
1) I usually recommend 1600MHz CAS9 as the minimum but having said that 1333MHz for most games shouldn't make too much difference at all. Also consider that memory testing usually uses a faster CPU as well (ram bandwidth requirement scales directly with CPU processing power).
If it's a pre-built system he'll have to weigh the pros and cons of what systems are available and I'd put 1333 vs 1600 near the bottom of the list in comparison to the GPU or other components.
2) BF4 on Ultra with a GTX750?
Possibly at a low resolution. A GTX750Ti which is faster gets 38FPS at 1600x900. "MasterDell" says 34FPS on Ultra but lists no resolution. When people say "Ultra" I think we should assume 1920x1080 not a low resolution.
3) Good system?
That's the real question. A GTX750Ti is 13% faster (stock vs stock) compared to a GTX750 so let's just use the results in the GTX750Ti 2GB benchmark here (about 20 games) to see how it scales and assume roughly 85% of the performance.
For example in Crysis #1 he'd get about 34FPS at 1600x900. Not only would I probably run at that resolution instead of 1920x1080 for this game but I'd also drop several of the settings to raise the frame rate further.
In some cases I'd suggest tweaking to maintain 60FPS (for 60Hz monitors) at least 90% of the time when using Adaptive VSYNC. You can research how that works if you want. VSYNC is really important if screen tearing is too bad otherwise leaving VSYNC OFF completely and tweaking to say 40FPS average might be better.
Summary:
The PC is just fine for almost any game provided you tweak the resolution and settings to achieve your desired frame rate.
*I can't stress this enough... TWEAKING the game settings is critical for the best experience. If aliasing is annoying run at say 8xMSAA. If not drop to 4xMSAA. If 1600x900 looks similar to 1920x1080 then use the lower resolution (depends a lot on the HUD elements mainly. Crysis 2 looks pretty good at 1600x900 but CIV5 which has small text not so much).
PHYSX probably should be disabled for any game with this card.
Use FRAPS, decide if you want VSYNC ON or OFF then tweak towards your desired FPS goal as mentioned before.
Whether it's a good deal is a different story and obviously a better Graphics Card will make the largest difference.