G,day Pilotpeter,
I did 2 seasons on the power lines for both Vic. and SA. back in the mid 90's
On the South Australian contract I flew a Robertson STOL kitted 172 and it was excellent. Flying into a slight head on breeze you could see a GS of 55 kts and thus give the observer a good look at the conductor, trees and tee's etc. and felt safe, guess indicated would've been around 65 kts. Probably need 70 to 75 in a non kitted version to feel comfortable, both with 1 stage flap.
Haven't flown VG's on a Cessna but from experience on others (mostly a pair of AT301's one with and one with out. I guess a 172 would gain about 5 kts at the low end and shed 1 or 2 kts at the top end. Your comment on improved aileron control is pretty true.
A bugger to wash though as Shawn pointed out. And if you do knock one or two off when cleaning it may mean you legally can't fly until fixed. Check that out yourself though.
Not unusual that when separation does occur it can be a little more pronounced. But this may well be type specific.
Neither company I flew for would condone steep turns at 70 kts, of course it can be done safely in the right hands, but how much extra money do you or the company make by reducing margins. The Vic's lost a crew in 95 to what appeared as stall incipient spin accident, and in the hands of respected pilot.
Your biggest asset for low speed flight will be a good set of hands with matching feet
Smooth as she goes and all that and know what the wind is doing. These won't cost the company a cent and they last and last and even get better with age.
M