I would wait until you get to level 59 and get the Ping G25s. They are the first iron set at that level with high trajectory, which makes all the difference in the world on elevated courses. The med/high trajectory irons just do not stick well, and you will have a lot of trouble getting on the greens on the more difficult courses without high trajectory irons. I've played 50 consecutive days and finally I am reaching level 59 today and will be buying them. I've used the starter irons up until this point.
If you decide to go with the med/high clubs and you do not like them, you can only sell them back to the pro shop for 25% of their original value. As far as meter speed, 4.0 is not a huge difference to 3.5....once you get to 3.0 and below its a big increase in speed IMO.
My advice would be to buy some wedges first. They will make the biggest difference in your game immediately. Either the lvl 38-39 ATV's or the lvl 41-42 Pings will serve you good. Get 2 right now, a 64 degree and a 60. Then once you buy your irons, drop the hybrid and add a 3rd wedge to your bag and account for the spacing between your PW and your 3rd wedge. For example, if you get the G25 irons, the PW will be 115 yards, So make sure the 3rd wedge you buy is between 90-100 yards. Space your wedges 15-25 yards apart from each other and learn to use the punch shot to fill the gaps in your yardage. Also, balls make a huge difference. Even the little 43 credit balls are a lot better than the starter balls. The spin on the ball and the trajectory of the ball makes it much easier to play with.
Believe me, I know it is very hard to wait to get new irons but that would be my advice. Just play at least 9 holes everyday and get your consecutive days played bonus of 880 xp everyday and you will be to level 59 sooner than you realize. I didn't expect to get there until middle of June, but I am gonna get there today and I will be buying the Ping G25 irons later today. It is definitely worth the wait to get the high trajectory irons. If you look at the pro shop, basically everything above level 59 irons are all high trajectory and for good reason. They are much superior irons.
While you are waiting to level up, take this time to learn how to use all the different types of shots in your arsenal. Punch, Pitch, Flop, Chip. I hated the flop shot when I first started. Since i bought my ping wedges, I have learned really how to hit the flop shot and it is absolutely deadly now for me within 30 yards.
Good luck and I hope this helped, as I had many of the same questions as you when I started out.