Really good toeside riders can ride upwind pretty much the same toeside as heel side, the majority can't get anywhere near as well upwind when toeside.
Im pretty crap at toeside because I never practice it, switchfoot just seems so much easier,better and more natural to me.
Just my opinion and I'm no expert but a board with not much tail rocker (or rocker in general) fairly wide in the tail, a nice hard sharp rail, lots of concave in the tail, quad or reasonably big finned thruster, ridden strapless and switch is the answer to going upwind.
The brand of kite and the way it is flown also makes a big difference, you have to let it fly and not choke it.
I use custom Oceanline Board which I must admit is loosely based on a proto BWS Drifter board that I had and loved for upwind ability (drifters weren't available to purchase when I wanted one so I had something similar made), they both take a while to get used to turning though.
P.S. My money is on Rowdy (or any good switchfoot rider over a toeside one).