Unless you're using a fan clutch with a flex fan, it's going to create more drag at higher RPM's than even a stock fan, and certainly more than an electric. If you're using a clutch with a flex fan, however ... why bother with the flex fan? Just get a metal stock fan replacement and be done with it.
FWIW, I'm still running the stock 1986 fan and clutch in my '86 GT 'vert and while it's got all kinds of little cracks in it (these plastic things crack within like 3 months of being installed new, it seems), it keeps things perfectly cool even on the stock crappy radiator with a stock-temp 195* T-stat and 110+*F desert heat temps.
JRichker can hopefully chime in with his wisdom on why running a high-draw electric fan is a bad idea on a stock 2G alt. Long story short, the stock alt is ALREADY busting its butt to churn out the 65 amps it already does, and putting on a fan that draws 40 amps at startup (most good ones will) means you're running on borrowed time before your alt gives up the ghost and/or you start eating up fuses/fusable links, perhaps even burning up wiring. (Stock alts are known for burning up at their main plug, anyhow. Crappy design by default.) Upgrading to a 3G alt not only gives you more breathing room for amps without draining your battery or risking the rest of your electrical system (and not needing to swap out alts more frequently), it's just an all-around better alternator, anyhow - better cooling, better bearing setup, etc.