I had a pair of Smith Bros. pushrods fail(one broke in half in the middle after bending and took the other one out bending it also) on a dyno test, it hurt the cam lobe and broke the top of the Crower solid roller lifter off I had ordered 3/8 diameter with .120 wall for a roller cam originally, I took the broken one back to Smith Bros and one of the shop employees made a comment that thier .083 wall 3/8 pushrods shoouldn't of failed that way They where not .120 wall like I had ask and paid for They replaced the two pushrods for no charge but didn't offer to help pay for the cam repair and lifters damaged. Smith Bros. was 5 miles awy from me back then, they have since moved thier shop 23 miles away now to Redmond OR. I fixed the motor and ordered a set of Manton Series # 3/8 diameter .120 wall thick pushrods of the exact same length and took them with me to the dyno, we made several pulls to warm the motor up with the Smith Bros. pushrods in it, changed the oil and filter. I checked the valve clearances and made several more pulls to make sure the motor was repeating. I changed the pushrods, no other changes, and that motor picked up 300 RPM to peak HP and 8 HP on that change Stiffer is better on pushrods when there are any doubts Years ago, circa 1968 or 1969, Don Prudhome(SP?) tested a set of tapered D&D pushrods in his old front engine top fuel dragster at Orange county dragstrip one Wednesady night, the motor picked up around 800 RPM and he had to lean the fuel system down around 20% was what was listed in the article that Hot Rod or Car Craft put out later about that test. The car picked up quite a bit also from that change, I don't remeber the exact amount but I'm thinking around .2+ ET and 2 to 3 MPH The RPM you shift at has a lot to do with what will work best for you also