I strongly suggest that you have your clubs fitted by a pro who knows what he/she is doing. Not all do. Here are a few things I believe to be true about clubs, club fitting, and golf in general.
Shaft flex and lie angle are the most important aspects of a club. If these two things are wrong you will NEVER achieve your potential in the game.
Clubs must be balanced across the set.
Clubs must be fitted on the range where ball flight can be observed by someone who knows how to interpret the data.
The short game is what you must master first. A good short game will allow you to score well even if your swing is out of sync on any given day. Therefore, your wedges and putter are the most important clubs in your bag. There is NO exception to this rule.
Money spent on lessons with someone WHO REALLY KNOWS THE GAME is the best money you will ever spend. I've only met a few who truly know what they're talking about and who know how to effectively teach.
The golf swing demands repeatability if you want to shoot consistently low scores.
The only club head speed that counts is the speed at contact. You must learn to relax, relax, relax when hitting a golf ball. Learn how to develop a swing where your maximum acceleration is at impact.
With irons, hitting down on the ball makes it go higher. Yes, even a 3 iron. It is easier to control a golf ball if you can hit it with reasonable height. This is what clubs are designed to do if used properly. Very few golfer can hit a low shot with a high degree of control. That's why even the pros marvel at Tiger's stinger shot. It's incredibly hard to do.