A long time ago, bopping along in my 180 Arrow at 10,000 feet, IFR in VFR conditions, from Boston to Kalamazoo. It had taken me 20 minutes to get that high -- 10 of that for the last 2,000 feet. Then, Cleveland Center asked me to climb to 11,000 feet for traffic...
Me: You mean it?
ARTCC: Sure do.
Me: Do I hafta?
Me: Okay ... but it's gonna take me ten minutes or better.
ARTCC: Okay, then if I ask you to descend to 9,000 for ten minutes, how long will it take you to get back to 10?
Me: Oh, 'bout the same, 1MV.
ARTCC: Okay, I guess I'll have to go to plan B.... 1MV, maintain one-zero thousand. United 123, turn right 20-degrees for traffic; American 456, maintain niner thousand for opposite direction traffic, 12 o'clock 10 miles at 10 thou; Trans World 789, cancel direct, turn right 250-degrees, and stop the descent at 0ne-two thousand ...