Well, you'll put more stress on a frame in one race than you will in a year of street use.
I've repaired quite a few street frames that have cracked under race use despite the fact that the bike was 20% lighter than in stock form.
Why else the bracing of OEM frames, the increase in front fork size, the bracing of swingarms, the increase in spring rates? Racer's learned a long time ago that in all but the "stock" classes, OEM frames won't hold up in the long run.
How often on vintage street bike do you brake from 90 to 40mph in about three seconds with the front end fully compressed and the back end skipping over bumps? How often do you lean the bike into a corner dragging the pegs at 90mph? Well...on a race bike figure about 50-60 times a DAY at typical race meet. How often do you crash on the street? Figure a couple times a year racing. Believe me, a vintage race bike with probably 50% more hp than stock, a front brake with twice the stopping power of stock, being ridden under conditions way outside the envelope allowed for OEM bikes....needs all the OEM frame strength plus some.
My 205 lb 175 will stand on the front wheel with a 200 lb rider, and lift the wheel changing into second gear. It's got 23hp at the rear wheel compared to about 14 for the stock bike, tops out at about 100 mph compared to about 80 for the stock bike. Believe me the frame is under more stress in one race that it would see in a year of street riding.
Thousands of racers for decades have been increasing the strength of rigidity of OEM frames so they can race them...they ain't doin it just for fun.
JohnnyB