In general, why would one not remove the any spacers under the stem? I am 5'10 with good flexibility( I can touch my toes, grab the bottom of my feet etc) and ride a 54cm Cervelo SL1. I have been Retuled by the shop that sold me the bike and put on a 120mm stem. When I asked about going lower he said he wouldn't recommend it but no real reason to why not. Another shop suggested that the bike was to small and we put on a 140mm stem. I feel more relaxed on the 140 and get sharp lower back pain with the 120 riding sustained periods of time riding low on the hoods. I thought droping the stem was more of a flexability issue than anything else. What other concerns are there?