Nice worl Eric
Now thats what I like to see, a dedicated astro imager willing to safeifice other things to collect as many photons as possible
to go from f5 to f10 would need 4x the exposure to maintain the same "deepness". making the subs 4x longer might mean too much noise (unless its cooled)and possibility of guide errors, so instead could simply do 4x the number of subs (would be an all nighter on one object).
A F10 SCT may do better as its a sealed tube wheras a Newtonian is not (unless active mirror cooling is used)
I once did a few 1/2 hour subs on the Helix, but I compared the result with 3x 10 subs and the single 1/2 hour shot was noisier. That was with my camera though, Ive yet to test the cooled DSLR on really long subs.
Scot