SNR reached within one hour of exposure with three separate cameras and three telescopes at f/5, so one hour per each filter, would only need 28 minutes and 48 seconds of total exposure with one f/2 telescope, or 9 minutes 36 seconds per filter, assuming everything else stays the same. So within the same hour only one f/2 telescope with one camera would allow to go deeper and reach a better SNR as opposed to 3 separate f/5 telescopes.
I don't want to come across as pushing this idea, it was just an alternative that could be cheaper and simpler. Personally I would not like an f/2 telescope for a range of reasons, but would be very happy with one 10" f/3 really well build Newtonian for imaging.
Honestly speaking, i tested that 135mm lens at F/2 and i didn't save time with it at all really, it was faster no doubt, but i was trying to shoot Ha LRGB, it took me like 3 nights to finish it all, because changing filters and checking out each filter focuser and re-cooling every time i change/checkout took me a while every night, and the target was running fast, it was like only 2 hours in the sky for best results, so that made my mind that having F/2 optics didn't help me really, even if it will give me better SNR the setup itself with one scope and changing filters and using SGP all killed me, now there are many options, and i already have 2 filters sets, so i was thinking which is more cheaper for me, F/2 setup or 2 scopes setup, already have 2 cameras now and filters, high quality filters, so i think having dual system will do it for me.
Starizona brought 0.65x reducer, sounds very nice one, if i use it with a scope of F/6 it will go to F/4, i do have 6" F/4 Newtonian, there is 0.73x reducer for Newt somewhere, that will put my Newt to F/2.92, i don't know how good or bad that will be, many keep saying about correcting and collimating, well, i saw one video about how to collimate Takahashi Epsilon f/2.8, was a headache for sure, but astrophotography is all about challenges and experimenting, i don't assume all members here or in the world all of them will just go and buy f/2-f/2.8 scopes, and i have to buy according to my budget according to me efforts according to my conditions and whatever, if someone is happy with F/2 and can afford it and accessories/extras with it that is fine, i don't have SCT so Hyperstar is out of my plan, RASA the smaller one is expensive, and with it i have to buy specific adapters and maybe F/2 highspeed filters, i prefer to use Astrodon/Chroma over highspeed filters actually, and i did see people have issues with RASA/Hyperstar, and fixing those issues also cost more, so to me it is like in all sides or options it will cost me money and time no matter what, now i go with what i started, RASA wasn't around when i started and that time i already went with like 2 filters sets so it was like fate to bring me to dual system over F/2 scope, and i still have 135mm and can't add another lens of f/2, also have 300 f2.8 lens and 85mm f1.8 and 50mm 1.4 & 1.8 already.