The viewfinder of the OM's is well known for being big and bright. I can't imagine how it could be brighter, as it looks about the same as looking directly at a scene. Contemporary lens tests showed the OM lenses to be among the best made. I'm not sure why you're fixated on fast lenses. The 35f2.8 and 50f1.8 are both tiny (the 35f2 is huge by comparison and takes a 55mm filter). If you want low light capability, the smooth shutter and mirror of the OMs easily gives two stops over other SLRs. I regularly shoot a 35mm at 1/15s, often at 1/8s, and sometimes at 1/4s - all hand held.
I shot primes for many years, as well as the 35-70f3.6. Recently I've gone back to my original 35-70f3.5-4.5. It is a small as any prime and gives excellent results. The only reason to carry two bodies is if you want to have two different films.
Final points --> The OM bodies are the smallest full frame 35mm SLRs. The replacements for the OM-1's mercury cells are readily available. I've had an OM-2 for 30 years and never had problems with the battery life.
There is also the late OM 2000. It's made by cosina so people don't consider it a real OM, but it has a number of benefits. It's very small, very light, has spot metering and usual shutter speed selector.
The 2-Series focus screens for the OM bodies are so bright that there is no difference between the matte area and the central split-image and microprism area. The reason is because the entire matte area of the screen is an even finer microprism mesh.
I absolutely love the OM system and have a few of the nicer items. It's all good, but some items, like the OM-3Ti, 35-80 zoom and 100/2 or 90/2 lenses are in a league of their own.
The OM system is the SLR that Leica failed to make.
You are feeling weak. You can hear them crying out to you: "O Emmmmmmmm. O Emmmmmmmmmm"
You are feeling woozy. Lightheaded. You are scanning Ebay for all things OM, looking, seeking. Yet not knowing why. Like birds flying north in spring, the call is upon you. You cannot resist.
An OM-1 was popular, maybe one of those can be bought. But wait! There it is... An OM4Ti. Nah, way to much for a fleeting love affair. But if you don't buy it, you'll not be sure that you've gotten the full experience.
Resist! Resist! You must resist.
"NO!" You cry out, "It must not be! I cannot do this!"
Auction closed, an OM body bought. Now for the lenses...