Both quite good choices to fly. The LA5-FN is a monster, as is the La7 and Yak-9U.
If you have a good feeling for how to fly the Yak, fly the La5/7 in the exact same manner. I am very aggressive in all of the above planes, so maybe I am not the best person for advice
First of all, these planes climb like the wind. The only plane in the arena that will outclimb La5 to 10K is G10 (I have tested this). Above 10K both lose a little bit of performance.
These planes will about outturn everything in the arena except the japanese planes and a good hellcat pilot (and the spits of course). And, couple this with the fact that they outclimb most everything in the arena (low at least) - you have a monster on your hands
Good luck, gimme a shout sometime if you ever need any help or training.
Nim (AKLarry)