I've been upgrading all my SLC's to the Maradyne fans which give over 1500cfm's per fan. They have made a huge difference in keeping the temps down.
http://www.summitracing.com/parts/mar-m122k
A set of upgraded Maradyne fans Model TA11A3001 - solved my idling/traffic high temp. run-a-way issue.
The do draw a lot of current so I had to direct wire to battery with a fuse and a relay with no issues since.
My temp gauge at a long traffic light would hit 220* - a throttle induced fast idle would help bring it down some but it was looking like a runaway train while I hoped the light would go green. Under speed never an issue even when the air temps were in upper 90's- summer heat. It's the low idle/slow movement of coolant in summer heat that was the problem.
BTW: Both fans come on at the same time - even with the A/C, which IIRC may only trigger one fan?? How the memory fades.... I have not had an issue since and do not use a shroud. 207 degree F is the GM ECM fan trigger temp. from the lit that came with my engine controller kit..