If by getting "into more playboating," you mean vertical moves (cartwheels, squirts, etc.) and especially if you want to include vertical moves on flatwater, then being at or over the top end of the suggested weight range is an advantage. This is not necessarily true for loops which require a certain volume of air filled boat relative to paddler weight for adequate "pop." Of course, if you can't bow stall a boat, then "pop" is irrelevant because you won't be flatwater looping. Paddling whitewater in playboats in which you are at or over the suggested high end of the weight range easily leads to punishment for poor playboater posture, poor technique, or inadequate attention. Additionally, if you have to move the seat too far back in the boat because of leg length and foot size, throwing the boat down to a bow stall will become more difficult because of the location of the majority of your weigth relative to the prefered pivot point for the boat.
At 5'4" and 140lbs, I play in an EZG42 (42 gallons) which I can flatwater cartwheel and which I enjoy using as a river runner as well as a park and play boat. I also have and like a Siren (40 gallons) which I would be surprised if someone 5'8" could fit in comfortably (unless your legs are pretty short for your height). Hull design matters as much as boat volume; I can throw down my EZG42 a bit easier than my Siren despite its 2 gallons greater displacement.
From my experience, if flatwater vertical capability is desired at 140 to 150lbs, I would suggest definitely staying under 50 gallons and probably even 45 gallons and under. I would also suggest looking at boats 25 inches wide or less (emphasis towards less). Besides the EZG42, I have spent some time messing about in a Kingpin 6.2, in a Vision 44, in a Skip, in an EZ, and in a Chronic. I didn't find the Vision 44 (44 galllons) or Skip (39 gallons) as easy to stern squirt as the Siren or EZG42 (I think more of a volume distribution effect rather than a total volume issue). At 47 gallons, I find the Chronic requires more muscle to double pump down than I care for and the EZ is just not going to happen. While I can throw down the Kingpin 6.2, I don't happen to like it's volume distribution for handling nor its leg positions for my comfort.
For foot and leg space, I think the Chronic, Project 45, Vision 44, 4twenty (small - 46 gallons), and Kingpin may offer more than the EZG42 and certainly than the Siren. I don't have foot space experience with the Jackson boats. I also don't currently have experience with the Fluid Nemesis (44 gallons), but it also looks like it might be a boat to consider at 140 to 150lbs.