Also many ignition boxes will retard the timing at higher RPM's and that is the reason for lost power not spark intensity. Is this common with MSD's or you are talking about your cheaper systems Crane/Mallory boxes never herd before  It's easy enough to dial back in with a grid... IF it is an issue. I got a grid when they were fairly new (2016?) and used it with a crank trigger, 6AL using the "Legacy" connector. I upgraded to the proper grid amplifier (7 series) after about a season and have had no problems. I did rewire the car, prior to install. I hear lots of issues with ign / electronics are caused by poor and or old wiring.
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
| 
