Has anyone modified their front suspension via different oil viscosity, different springs?

I did the Wilbers shock 3 years ago and it made a huge difference in comfort, plus it kept the original rear Metzeler rim protector in contact with the bumpy pavement around here. When a fresh set of Road 5’s became available, my mechanic mounted them and replaced the fork springs with Wilbers units. I went with Bel-Ray 7 wt. (cSt 29) to replace the Honda 10 wt. (cSt 35). Might go 5 wt. next time. Conveniently, it took exactly 500ml in each fork tube to set the air gap at the prescribed 130mm. Front end feels better controlled but only a moderate change as compared to the tires and shock. All told, it’s a whole new bike. Comfortable and handles great. I’m 5’5” and 150 lbs.

You mentioned it. The springs helped but not a complete solution. Try this link.

The YSS seems to be the flavour of the day on this forum. It is relatively inexpensive and apparently well-built. It comes with a spring that is about right for a 170 lb rider, so most riders are cranking in a lot of preload. Not ideal but still a big improvement over stock. But 350 pounds? I would start by calling the people at www.beemershop.com. They carry YSS, Wilbers and other brands. Perhaps they could substitute a heavier spring on the YSS (Wilbers shocks are built to order). Then there is the matter of remote hydraulic preload adjustment. Anyway, I would get some options, then decide.