Non greasable are definetly stronger!
Get Moroso or other quality H.P. joints and don't worry about a loop. Loops are needed mostly with: slicks, Big Blocks, trans brakes, roots blowers, and stick shifts.
The only time that I ever hurt a drive shaft in 50 years of racing and running low 9 and 10 second street/ strip cars, was in my 1968 Nova. An 8/71 blown, ported, roller cammed, BBChevy at 14 lbs boost, Hoosier biggest tires that I could fit into the wheelwells, and seriously worked suspension, on a brushed concrete freeway on ramp. Grabbed 2 ND gear (manual valve body built TH-400) at about 55 mph, pretzled the driveshaft, about 4 complete twists! Never hurt the Moroso U joints! It didn't even twist it in half! Just shortened it enough to slide out of the transmission spline!
Your results may vary.....
TIMINATOR
I hung that on the wall at my shop for years!