Of the two, aspirin appears to be metabolically better as a safe exogenous substrate for reducing prostaglandin-e's in the inflammatory cascade of events leading to pain. TR's are at max-dose at 6 per day or 2 taken with each meal. ADVIL's NSAIDS-Ibuprofen has been known to adversely reduce kidney response to hyperthermic conditions and contribute to kidney failure in predisposed athletes during heat conditions. Beware also, aspirin dose should be enteric-coated for a 500 mg. or any dose may create gastric stress, which can turn 200 miles into DNF...or worse. Safe dose use is individual and nearly impossible to specifically determine. For sure, I will not recommend either for prolonged or high dose application to resolve pain above the manufacturers dose directions, especially in athletes enduring hyperthermic stress in a 10-12 hour event. I know of athletes who pop the NSAIDS like candy, but I also know that a few of them end up in the hospital with kidney shutdown, dehydration, and hyponatremia. Ideally use as little aspirin as you can and only what the package directions state. Ecotrin in 350-500 mg. units, once every 4 hours is, as I recall, the upper recommended dose. I would consider moving the seat UP in 2-4 mm. lengths as a trial application, while also moving it back to take some of the stress off the knee. Pedal float is another concern, I will simply mention but not detail, since I am not a bike expert etc. Orthotic corrections for down stroke pronation balance is another concern to share.