The righty/lefty situation on bull-pup designs is most definitly a pain in the ass. However the actual assembly on the FAMAS makes it easy enough to replace the bolt with a South Paw style system, the only drawback is in a CQB/C situation when you're shooting around corners and quickly have to go from Strong hand to South Paw firing. Essentialy what it comes down to is that although the bull-pup design is most excellent, ecspecially in the extra barrel lenght you have in similar style weapons, ie; M4A2 and FAMAS, you lose the ability to use it in odd situations.
I found that in my expierence in firefights its a better idea to go with a standard layout weapon such as the M4 series due to its capability to be used in almost any scenario.
As for the SCAR...It's the same idea as the M4 series weapons, however more 'futuristic.' If you're look for a good multi-cartridge weapon platform you should research the MASADA. It will go from STANAG 5.56x45 to the Russian 7.62x45 rounds. Both are exceptional platforms, however the MASADA is much better made for CQB to extreme long range combat.
Side note: Be careful with a SCAR. If you have previous expierence with an M4, you'll know that it's safety-single-full.
On a SCAR, it's full-single-saftey. There's been alot of Accidental Discharges in test units because of this.
If you're further curious about optional weapons platforms, let me know..