I use a lot of rl16 and h4350 with 6.5 cm. The velocity thing is definitely true, however, I also find rl16 to be less temperature sensitive. However, both are great in this department.RL16 is more temp insensitive then H4350. I prefer it over H4350 or just about any powder for the 6.5CM. Plus you get a speed boost with it over H4350. 100+ FPS is not uncommon when comparing the 2 loads at full boogie loads.
H4350 is definitely cleaner than rl16. I get similar accuracy with both using 140s.