It's not a large difference, in fact, I doubt any shooter would notice much of a difference at all. I wouldn't make that your deciding factor on which platform you choose - essentially, they are still the same and can be interchanged easily.
To add to the Accuracy:
The 5.1 may have an additional advantage, as the front and rear sights are further apart, to give a slightly increased degree of accuracy. Plus, the Bomar rear sights of the 5.1 are adjustable, whereas the 4.3 is fixed.
Again, it's not an issue... down the line, you could always switch it up... or if you want, I can get you custom machined 4.3 length slides with rear dovetail sight cuts made to fit the 5.1's Bomar adjustable sight or if you wanted to get real nuts, 10" long slide/barrel/compensator setups... but you also have to realize that will affect maneuverability. lol.