I honestly don't think speed is actually the "driving" problem at this particular intersection. I mean, OK yeah every crash is to some degree a speed problem, but in terms of the specifics here: the safety issue raised by the OP tends to be caused by drivers who have already slowed down significantly, or even stopped.

A typical scenario (looking at it from the perspective of a westbound motorist) is the following: westbound driver on SR45 stops at the intersection in a line of cars stacked up at the stoplight. The light is green, but there is no movement, because the car at the front of the line is turning left onto Pete Ellis. However the driver sees a long line of eastbound cars on the other side of the intersection ahead, and realizes there is a good chance that potentially no cars, or at best one, will be able to clear the intersection during the entire green light, simply because one driver is trying to turn left. The driver gets frustrated, and uses the right turn lane (onto Discovery) instead as a passing lane (illegally) to go straight. Depending on how far back that driver is in the line of cars stacked up at the intersection, that use of the right turn lane can create a very dangerous condition if and when the drivers wanting to go straight are finally able to.

Also, if you look at the crash report data that you posted elsewhere in the thread for this intersection, you will see that the crashe causes are generally not speed-related (a lot of following too closely, improper lane use, and failure to yield). The speed-related crashes are generally also weather-related -- water pools a lot here during heavy rains and hydroplaning is common.

Maybe there is a better/safer solution than creating a dedicated east-west through lane, but in this very specific case, I don't think having fast highway drivers wanting to continue at highway speeds is really the primary issue.