At D3 Press can be devastating if you have a weak schedule, however when you start to face teams of similar athletic/speed caliber or better it can be exploited, and can cause you to foul a lot!
I'd say Press is most useful at D3, however Man is very effective, doesn't require as much depth and you won't foul as much. Whereas Man is probably better for D2 and D1.
When you switch defenses it pretty much makes your entire team start as freshmen, depending on how how many recruits you can get will also affect it. I'd say 2 seasons to be competitive, 3 before you can make a deep run, you can do it faster with grabbing juco's/transfer who have your offensive IQ and press IQ.
It might also be worth it to continue playing zone while you have the majority of your team with zone IQ.
I see both teams you have are zone were you planning on switching both to press?
And remember if you do switch to press you already said it but you need to recruit more ath/spd/def for your teams, you're recruits are generally pretty weak in those areas. Top teams usually average 50-60 team ath/def and 45-55 in speed