Beam strength and TPI are critical. Itchy imagine pushing on a rope, doesn't work very well...right. Well, when you saw, the work is interrupting the rotation of the blade. ..especially if the saw dust accumulates because the small teeth can't clear it out fast enough.
As the lower wheel tries to pull the blade through the work, the tension changes on the rest of the blade. That's where you need beam strength,(resistance to bending) and additional tension to keep the blade running true. Proper tension is really more important than the blade guides supporting the side of the blade. The video at the bottom of the page shows that process: http://falbergsawz.com/
When the blade starts to wander and you have to compensate by allowing for drift, the set of the teeth on one side is worn more than the other. You should be able to set a fence to a properly trued and adjusted bandsaw and make parallel cuts with no drifting issues.
When you do get your new blade take a diamond stone or sharpening stone and round off the back of the blade and reduce the sharp edges. This will allow you to turn the work easier when making curves.
I have a "few" bandsaws and leave one set for resawing with a 3/4" 3 TPI blade. Others have 1/2" or 3/8" blades for curves. A sharp blade with 3-6 TPI depending on the width and thickness of your material will work well for you. I'm not a bandsaw expert by any means, although I do weld my own blades from bulk stock off the rolls in 100 ft lengths. I have a couple metal cutting bandsaws also. Metal cutting blades I use have 18 TPI, much less than wood cutting blades. Thinner metals require more TPI so the blade won't hang up on the space in between the teeth. Even today I cut a 3" x 3" x 1/4" angle iron to length.
Slow but sure, it just kept cutting...lots of hours on that blade too.
I believe with your new riser the tension indicated on the spring washer will not be adequate for the longer blade. There is a "flutter" technique for setting the tension. Where you back off the tension will watching the blade until it starts to flutter, then tighten it back up about 1 turn.