My trail is 8 inches an 9.5 inches, no problems at all. It's pretty stable and it prefers to go straight, so its not exactly a road carving maniac. At Low speeds, the front end will want to lay over, but you get used to it quickly. Dont get me wrong though, my bike will still cut the corners and is still manageable at low speeds, but it's definitely not a sport bike. It will want to stay upright instead of leaning into the turn when you tell it to, so you have to plan your moves a bit ahead of time.

Sugarbears setup is typically to create near 0 trail. This is so that he can have loooong front ends that still handle really well. The turning radius still sucks, but it is responsive between its limits. The rockers are made to lower the legs of the springer thereby dropping the trail length significantly.

If you run tubes, you might see other problems. If you are running thinner (stock diameter) tubes, the sliders will start to bind as the rake gets higher. You will basically have a rigid front end. I have a set of early model tubes with early lowers and they barely provide any cushion at 46 degrees. The later model lowers are longer and better suited for more rake. Keeping them clean, full of the correct fluid, mic-ed to the appropriate tolerances, etc. will keep them working at they're best for you. Youll notice the loss of suspension as you increase your rake though.

Your springer can be adapted to the rake to compensate for the increase in trail. Make longer rockers, drop the legs down in relation to the front axle (mind your frame level and clearance). But when you make your rockers longer, be sure to check the rate in your springs. You will be applying more torque as your rockers get longer and your suspension will soften up significantly. You might need to go with a higher spring rate if you make your rockers really long. Also, if you are want to carve hard on the curves, you might want to look into a dampener for your front end. You're suspension being undampened right now will start to oscillate as you increase the relative downforce on the bike (i.e. centripetal force, that compressing feeling you get when you go around a hard turn). This oscillation will make you wiggle off of the curve. This might just be another thing you can get used to. Just another limitation to a springer front end.

Build it, then tame it.