The thing with "F7" is it starts off coarser, but breaks down faster, whereas the "C" isn't as coarse but the particles also don't break down as quickly. The end result is a more consistent polish IMO with the "C"...not as big of a deal when compounding because you go over each area several times, but it is when using the Cyclo and only going over an area once or twice.
I also think temperature & humidity can make a difference...if you already have some of both, give them both a try and then see which you
like better. If you have to order it - get 1/4lb of each then a 1lb of the one you like better in a second order. With your trailer being longer, you will probably use the extra 1/4lb. And you'll get the smaller jar to use while polishing - less likely that the whole lb. dries out or tips over....we always put some in a smaller container, rather than using it straight from the big jar.