i have owned grados for years, and loved everymodel i owned. i started with the 60's when i went to college - used em both on the stereo and w/ the pc, had to send em in for service at one point (by the way, awesome customer support - really a great thing when the founder of the company and head researcher takes time to email you about your problem w/ the cans) anyways, i decided to do the upgrade to the 80's. best $25 or 30 i've ever spent. they were even better imaging and much nicer on the bottom and top end. needless to say, i loved em even more. a few years later, roommate was borrowing my 80s and got his car broken into, lost my cans as well as alot of his stuff, so he decided to be nice and bought me a pair of 125's. all i can say is wow, these things are absolutely amazing.
i have never owned a pair of senns, so i can't comment on super long term useage, but from what i've listened on friends, i haven't been overly impressed w/ any that i've heard that weren't outrageously priced. then again, now, i'd take my 125s over almost any price senns.
short side of the story, if you like your grados, then stick with them, you won't be dissappointed. the jump to the 80s is worth it in my opinion, and if u can splurge the 20, do it! the customer service, if nothing else has me a grado customer for life.
as previously stated though, if you're that wavering, go into a good audiophile shop and listen on both of them for awhile, most places won't mind you just sitting and trying to determine your choice (hell, i sat in a shop one day auditioning speakers for almost 8 hours and nary a complaint or rude staffer) so go listen and enjoy!
