Stock swaybars are like 19mm IIRC. Aftermarket range from 22mm to 26mm depending on the company and whether it's for front or back. MachV
sells both front and rear but their front requires some modification of the brackets to make it work. I think the simplest solution is to drill and tap the sub-frame which isn't really that bad if you're handy. If you can find a WL front bar (NLA) they come with a super thin bushing and can be installed using the OEM bracket with no modifications.
I run a Whiteline 22mm front bar and RM 15/16" (23.9mm) rear bar and I highly recommend this combo. I think it makes a huge difference for turn-in and cornering without being so stiff that it inhibits ultimate lateral grip.
Since anti-roll bars inhibit independent wheel motion you'll never notice the effects of a sway-bar while moving in a straight line. When you lay into a corner, however, they couple the inner wheel to the outer wheel which makes the outer wheel behave as though it had stiffer springs than are actually mounted. It is possible to overdo it but for the size of bar that we're talking about I don't think you need to worry about that. If you got some crazy huge custom bar you might find that there was some disadvantage but for the sizes that are readily available I don't think there is any downside.
I would argue, however, that the benefits of an anti-sway bar are somewhat wasted on a car with 4ws still installed. Please refer to my epic MSPaint drawing.
Imagine that you're in the brick shaped GVR-4 and that the car is headed down the page rotating counter clockwise around the oval track. At the point where you are the track is at it's highest curvature and to follow the track you need to be turning on the red circle at this point. The front wheels are oriented to accomplish this with the rear wheels pointed straight ahead as indicated by the little red lines. Now as you smoothly pass over 25mph your 4ws kicks in. The rear wheels suddenly point into the turn and are now aligned along the little blue lines. This instantly increases your turning radius and moves the focus of the turn forward with respect to the vehicle. So, where you were safely on the red circle, you're now on the blue circle. The blue circle doesn't match the curvature of the track so you overshoot and hit the tirewall (fire-hydrant). In order to avoid this you need to be able to suddenly turn in even harder to get the vehicle to rotate and get back on the red circle. But that's only possible if you aren't at the limit of traction. But, if you aren't at the limit of traction then you're not taking corners hard so why do you want anti-sway bars in the first place?
That is all to say that you should get anti-sway bars 'cause they're awesome and you should also ditch your 4ws system because it is the suck.