Most manufacturer 'on the box' claims of 350fps are kind of: '350fps when downhill, with the wind behind it, and with an ideally weighted BB...', so I'm sure it will pass the chrono test under 350. I bet it will be more likely to chromo at around 325ish.
Difficult to acquire targets quickly with a scope, so not always ideal for a fast-moving skirmish, easiest to aim accurately with open iron sights, but slightly quicker to get 'in the general direction' in order to rapidly return covering fire with a red dot sight. Red dot sights can be a bit off-putting sometimes in bright conditions, so if it has a green dot mode, put it on that.
Much of the time in a skirmish, you'll be using something like an M4 as an assault rifle in the truest sense of its name, i.e. someone fires short full auto bursts to keep their heads down whilst someone else tries to move up in order to get in grenade range, or in a position to create a vicious crossfire to allow some of your people to final assault the enemy position whilst they are pinned down and then nail them with CQB weaponry, or your assault rifle on full auto. In those circumstances, pinpoint accuracy isn't actually as important as getting shots to hit in the general area, so it pings off stuff all over the place and makes people duck for cover, and it always does make people duck when a crapload of BBs doing 300+ fps start bouncing around their position.
Unless you have some decent quality quick-release mounts for your scope, which ensure it goes on there in an exactly zeroed position you've previously set up, it will be difficult to ensure your scope is zeroed when you put it on on the day, without some time to check it, which you may not have. So if it were me, I'd stick the Red Dot sight on, zero that in, then see how you get on with it at the skirmish, and then if it's not suitable, just take it off and go with the iron sights.
anyway, whatever you decide upon, make sure you have fun, which is the main thing.